Health-related behaviours affecting diet, weight control and physical activity are important for long-term cardiovascular health but behaviour change is difficult to initiate and even more difficult to maintain. We have developed a health promotion program, in which social support has a key role, to encourage a prudent diet, weight control and physical activity. Behaviour change is based on evaluating initial behaviour, weighing up costs and benefits, assessing barriers to change and goal-setting. We first evaluated the program in couples beginning to live together, a group chosen because of the risk of weight gain and decreased physical activity after marriage, readiness to change behaviour at that time in the life course and the opportunity to use partner's support in achieving behaviour change. In an initial short-term study with 39 couples, intake of fat and take-away foods decreased and consumption of fruit, vegetables and reduced fat foods increased. Physical activity increased and there was a 6% fall in blood cholesterol. Further evaluation in 137 couples included assessment after 12 months. A decrease in fat intake and increase in physical activity and fitness seen at the end of the program persisted 1 year later. Lower cholesterol and a trend to lower weight gain and lower blood pressure were also maintained after 12 months. We have modified the program aiming for weight loss, improved dietary habits and increased physical activity in overweight treated hypertensives, supported by their partners. Decreased intake of energy, total and saturated fat, and weight loss seen at the end of the 16 week program was significantly greater in the intervention group than with usual care. Blood pressure fell in the program group at the end of intervention and, in men, withdrawal of antihypertensive drugs was significantly associated with the intervention. Weight loss and a decrease in waist circumference were maintained in the program group up to 16 months after entering the study. This program has the potential for wider application in other at-risk groups.