Two American cardiologists, Meyer Friedman and Ray Rosenman, were the first to describe the individual most vulnerable to stress. He - or, less frequently, she - was christened the Type A personality, and the doctors claimed Type A was at greatest risk of coronary heart disease.

Other scientists have since produced evidence for and against Friedman and Rosenman's clinical conclusions, but for more than 35 years the idea that you were a Type A or Type B ( more correctly a non-type A) has informed our understanding of stress. It is perhaps a simplistic approach to a complex issue, but few psychologists would disagree that certain people with common characteristics, are more likely to suffer stress than others.

Type A behaviour is characterised by high achievement, aggressiveness, strong commitment to work, competitiveness, impatience and a chronic sense of time urgency. It has been variously described as a coping pattern, a learnt style of behaviour, or as a personality trait. Some psychologists believe that Type As are driven by a strong desire to control events and become highly stressed when they can't, or when the situation they are in is ambiguous; others suggest it is due to low self-esteem compensated for by constant achievement in the workplace

Stephen Palmer, a chartered psychologist and director of the Centre for Stress Management in London, says the evidence for the latter is persuasive. "Their belief system is, 'I must at all times perform well. I must at all times succeed in what I do, and this will prove how valuable I am'."

There is a sub-group of Type As - the rigid perfectionist - who are particular casualties of the Nineties, and who make up the majority of the "burn- out" cases Dr Palmer sees in his clinic every day.

"The Eighties was their heyday. You could be perfect [in the workplace] because you had the staff and the resources," he says. "With downsizing and delayering in the Nineties, there are less people doing more work. Instead of realising they have less resources and accepting this as a limitation, the perfectionist believes that he or she must achieve the same results as before. In the short-term they may be able to do it but not in the long-term. They will suffer anxiety, depression, and anger - and eventually burn out. Most of the people I see are no longer able to work."

For Type As, the key to dealing with stress is the realisation that behaviour patterns can be changed and new ones learned, according to Nick Kitchen, a "former Type A ex-advertising executive" who is now managing director of Opera Communications, a training consultancy that offers stress management courses.

"What it comes down to is choices. At any stage you make certain choices and lay down patterns of behaviour and habits which inform other choices."

Often these choices start in childhood. Some children will develop a "rescuing" style of management. For example, they learn that life is better if everyone is happy and they will go out of their way to ensure this is the case. In adulthood, this can result in "phenomenal stress internally", Mr Kitchen says. Other children will adopt "defensive" management techniques which trigger their own problems and stress in later life.

Type B, also known as the "hardy personality," is based on a theory developed by Suzanne Kobasa in 1979. The behaviour of the "hardy individual" is characterised by flexibility, an ability to adapt to changing circumstances because one of their fundamental beliefs is that "change is the normative mode of living", says Dr Palmer.

Hardy individuals have a strong self-belief and commitment to work, family, relationships, and social institutions. They manage to maintain a balance in their lives which is unknown to the Type A personality. They also show a realism in that they believe they have control over events and will seek explanations for why something has not gone according to plan, focusing on their own role in this in an objective manner.

"Hardy individuals would tend to perceive difficult situations as challenges, and not as stressful, using cognitive coping skills to keep stressors in perspective. Unpleasant events would be interpreted as opportunities instead of threatening situations," writes Dr Palmer in his book Developing Stress Management Programmes.

One of the great, unrecognised truths of working life is that the most successful people are those who limit the stressors in their life, says Mr Kitchen. "Look at Richard Branson. He is certainly not stressed - although lots of people around him might be."