Numerous studies examine inequalities in health by gender, age, class and race, but few address the actions of primary care doctors. This factorial experiment examined how four patient characteristics impact on primary care doctors' decisions regarding coronary heart disease (CHD). Primary care doctors viewed a video-vignette of a scripted consultation where the patient presented with standardised symptoms of CHD. Videotapes were identical apart from varying patients' gender, age (55 versus 75), class and race, thereby removing any confounding factors from the social context of the consultation or other aspects of patients' symptomatology or behaviour. A probability sample of 256 primary care doctors in the UK and US viewed these video-vignettes in a randomised experimental design. Gender of patient significantly influenced doctors' diagnostic and management activities. However, there was no influence of social class or race, and no evidence of ageism in doctors' behaviour. Women were asked fewer questions, received fewer examinations and had fewer diagnostic tests ordered for CHD. 'Gendered ageism' was suggested, since midlife women were asked fewest questions and prescribed least medication appropriate for CHD. Primary care doctors' behaviour differed significantly by patients' gender, suggesting doctors' actions may contribute to gender inequalities in health.