The appeal follows the appearence of a 49-year-old Romford man at Havering magistrates' court, east London, on Thursday charged with the indecent assault of a 19-year-old woman he was treating with hypnotherapy.
He was said to be 'acting as a doctor purporting to be carrying out an examination for kidney stones' when the alleged assault took place.
Detectives believe women in the Romford area may have unwittingly become victims after seeking help with smoking, dietary problems or stress. They appealed for women, who might not remember anything, to contact them with information.
Officers who raided the man's home found 30 home-made videotapes, some showing women apparently under hypnosis allegedly being subject to sexual assaults. Some women appeared to have taken drink or drugs.
Police said they were appealing to women who had visited hypnotherapists in the area to come forward so that detectives could identify the women on the tapes, find out if they were aware of what was going on and whether they had consented.
Last night police said more than 30 women had called the hotline. Detective Sergeant Colin Threadgold of Romford police said yesterday he had watched two videos and 28 had yet to be seen. The two videos were of a number of women of various ages.
'They show women, in my opinion, under hypnotic control who are having some very strange things done to them. It would amount to serious sexual assaults if the ladies were to complain. Some of these women may not know anything has taken place. It is a question of putting the people and events together,' he said.
Scotland Yard said that police who interviewed the man felt they were being hypnotised. He is believed to be married with two grown-up children.
Scotland Yard also said his finances were being investigated.