Health promotion has been expanding to include potential effects of the spouse. A randomised controlled trial examined effects of involving husbands in a self-regulation programme designed to increase wives' performance of a health behaviour (breast self-examination, BSE). Participants were 140 couples (women ages 24–55). At baseline, women received questionnaires, information about breast cancer and BSE, and instructions to form an action plan for BSE performance. For half the women, the instructions called for involving the husband. Three months later, all women and husbands filled in follow-up questionnaires. The programme was very effective in increasing BSE in both groups. The husband involvement intervention contributed to this increase only among husbands who reported encouraging their wives. Involving husbands in the programme also resulted in their greater knowledge of their wives' BSE performance and encouragement of wives' BSE performance, according to their own and their wives' reports. The greatest changes in women's behaviour were apparent among women who at baseline rated their husbands as not involved in issues related to their health. The findings suggest that involving spouses in health promotion interventions affects their knowledge and behaviour but may need to be tailored to the characteristics of the couple's coping with health matters.