The hypothesis that 6 months after acute myocardial infarction, adoption of secondary prevention activities would be higher, quality of life better, and blood cholesterol lower in patients randomly allocated to a mail-out intervention program than in those receiving usual care was tested. Patients were aged < 70 years, admitted to hospitals in and around Newcastle, Australia with a suspected heart attack and discharged alive from the hospital. Cluster randomization, based on the patient's family practitioner, was used to allocate consenting patients to an intervention or usual care group. A low-cost mail-out program was designed to help patients reduce dietary fat, obtain regular exercise by walking and (for smokers only) to quit smoking. Supplementary telephone contact was also used. In addition, a letter was sent to the family doctor regarding the benefit of aspirin and beta blockers for secondary prevention. Of eligible patients, 71% participated, and 79% of the 213 intervention subjects and 87% of the 237 usual care ones returned a 6-month follow-up questionnaire. Self-reported fat intake was significantly lower, an "emotional" score obtained from a quality-of-life questionnaire was significantly higher in the intervention than in the usual care group, and "physical" and "social" scores for quality of life were slightly higher. Blood cholesterol level and other variables were not different between the groups at 6 months. Simple low-cost programs providing support and advice on lifestyle change may be beneficial, particularly in improving patients' perceived quality of life.