The prevalence of coronary prone behaviour, type A, was investigated in a population sample of 1,958 men and 2,224 women aged 30-64 years representative for all people of that age actively employed in Finland. Type A behaviour was assessed by the Jenkins Activity Survey. The mean values of the standardized AB scale were -5.6 in men and -5.8 in women. Type A behaviour was strongly associated with the level of education, occupational group and the socio-economic status achieved. However, it was not related to the conventional cardiovascular risk factors. The prevalence of coronary heart disease was statistically significantly associated with type A behaviour.