WHEN Susan met Michael for the first time it was like the beginning of a great romantic affair.

They had spoken on the phone and she had liked the sound of his voice. Before going to stay with him she felt excited and apprehensive. 'I wanted to look pretty, to make the best possible impression. He was very nervous too. When I arrived he was charming and gentlemanly - taking my coat, fussing around. We talked for hours. Over dinner we kept staring at each other: he kept telling me how beautiful and talented I was. I found him incredibly interesting. At the end of the evening we were lying by the fire looking at photos. We fell asleep in each other's arms.'

Susan says will never forget that meeting - which was not with a new lover but with her father. She was adopted at birth, and had always wondered about her real parents: finally, at the age of 22, she decided to look for them. After two months of phone calls and letters she found her father, living alone in Ireland. Several emotional conversations later she went to visit him.

'There was an immediate sense of recognition. He looked very like me, as I had hoped - the face, the gestures. He had the same sort of physical characteristics as an old boyfriend I'd never really got over. There was a very strong sense of having found each other at last. Towards the end of the weekend I began to realise it was getting very emotionally intense.

'I knew I felt attracted to him, which really scared me. I never talked to him about it, but I believe he felt the same.'

Susan was lucky - the confused yearnings she felt towards her father dissipated over the following months, and she was able to build up a normal relationship with him. But her experience is by no means unusual among adopted people meeting their natural parents for the first time, as research by adoption agencies is beginning to reveal.

The Post-Adoption Centre (PAC), a counselling service, receives hundreds of phone calls a year from people seeking to trace their adopted children or natural parents. The Adoption Act of 1976 gave all adults the automatic right of access to birth records, and since then the number of reconciliations has increased steadily. New proposals published by the Government last October will also put more onus on agencies to help locate relatives.

But not all reunions go smoothly. Feelings of disappointment and rejection are the most common problems which the PAC's counsellors try to help with. But according to Phillida Sawbridge, director of the PAC, more people are contacting agencies such as hers for help with the feelings of attraction, rather than rejection, which they are experiencing towards new-found relatives. She says that women in their early thirties who had a child adopted in their teens are particularly vulnerable, as are siblings meeting for the first time.

Why this attraction occurs is hard to pin down. Dr Maurice Greenberg, a consultant psychiatrist, has recently begun researching the syndrome for the PAC. He says that the nature of the initial meeting, the striking physical similarities between the two parties, the fact that both have missed out on childhood bonding and the chance to develop normal cultural taboos, can all contribute. 'Some people just feel overwhelmed. It's like adolescents falling in love - reality is suspended and fantasy takes over,' Dr Greenberg says.

Barbara Gonyo, an American whose son was adopted at birth, launched a counselling agency, Truthseekers in Adoption, after her own struggle to cope with strong feelings for her son when she was reunited with him in his mid-twenties. She is also hoping to publish a book based on her experiences and those of the hundreds of people who have written to her with similar stories. Many of these confess that they have slept together, some are living together, some have even married illegally. Others talk of the 'torturous guilt' they feel. Some had found their own ways of solving the problem: a grown man was bounced up and down on his mother's knee; a brother and sister stayed with their grandmother and played together like children.

The powerful feelings of reunited relatives can produce shock waves through the whole family. Nicholas, a married professional man with four children, has been receiving counselling from the PAC since he left home, unable to cope with his wife's relationship with her new-found son. Their conduct, he feels, is 'more like two lovers than mother and child'. Nicholas felt he and the rest of the world were excluded.

'My wife would spend three hours on the phone to him every night. Then, when he came to stay, I'd walk into a room and find them embracing - they would break apart when they saw me. The atmosphere was awful. I felt immense loneliness. I was totally superfluous: I was particularly hurt when I saw her showing him affection which I felt I'd never received from her. When I put my foot down, he moved out. But then she just fretted until she saw him. She couldn't bear being separated from him.' His wife's son was also married and that too is now over.

Existing relationships have to be 'very sound' to withstand such a trauma, says Dr Greenberg. The most important thing is to ensure that parted relatives are properly prepared for their reunion. 'They should be careful to meet on neutral ground, preferably with other relatives or friends present, and swap photos first so the initial shock is lessened if they are strikingly similar. They should try to refer to the person as their brother or mother. Geographical separation can help too.'

Normally well-balanced adults, like Susan, will gradually recover their emotional equilibrium without disastrous consequences. The danger point in any adoption reunion comes when the two individuals involved create a boundary around themselves and exclude others. 'Then,' says Dr Greenberg, 'everything can be put in jeopardy.'

The Post-Adoption Centre, 8 Torriano Mews, Torriano Avenue, London NW5 2RZ, tel: 071-284 0555