The maintenance of good health in the well population is an important goal of modern general practice. This often takes the form of encouraging patients to lead healthier lives, particularly where diet, exercise, alcohol and smoking are concerned. The fact that many people appear not to follow 'healthy lifestyle' advice suggests that more needs to be known about how relatively simple health promotion messages are understood and evaluated by the lay public. In this paper, findings from three independent qualitative social research projects in Scotland and Wales are analysed together. As qualitative social research is usually carried out with small numbers of informants, the work reported here represents an unusual opportunity for a large amount of interview and observational data to be analysed. The findings indicate that lay evaluation processes use subtle ideas of balance to weigh up the desirability of behaviour change, and that the practice of 'trading-off' positive and negative aspects of health-related behaviour is widespread. Conclusions for health promotion in the general practice setting are drawn. In particular it is suggested that the local knowledge held by the primary care team, and the opportunities for one-to-one interaction which exist in the general practice setting, are extremely important resources, given the highly personal nature of public evaluations of lifestyle change.