We present the results of a behavioural genetics study on response profiles of autonomic measures (heart rate, blood pressure, and galvanic skin level), under ecologically valid, stressful conditions. Where response profiles of different physiological variables are the object of study, and when daily life stressors are taken into account (Turner and Hewitt, Annals of Behavioral Medicine, 14 (1992) 12-20), autonomic responsiveness to psychological stressors is thought to be an inherited trait. The participants were 100 female twin pairs, 57 monozygotic and 43 dizygotic twin pairs. Participants watched eight films with a stressful social content while autonomic measures were continuously recorded. Results show that the heritability coefficients of response profiles of autonomic measures are almost twice as high as that of single variables. The results further show that genes exert their influence on physiological behaviour not only directly, but also indirectly, by influencing the idiosyncratic relation between a person and his environment.