A total of 216 patients attending either the British School of Osteopathy, a large acupuncture centre (City Health Centre), the Royal Homeopathic Hospital or a large general practice in South London completed a questionnaire on the perceived efficacy of orthodox and complementary medicine. The questionnaire covered 1) demographic information and experience of complementary medicine; 2) the Health Locus of Control scale; (3) attitudinal variables: belief in the importance of a scientific base to medicine, the importance of psychological factors in illness and the possible side effects of modern medicine; and 4) ratings of the perceived efficacy of acupuncture, osteopathy, homeopathy, herbalism and orthodox medicine for 16 illnesses, divided into four categories: major, minor, chronic and psychological. Whilst there was no difference between the four groups, health locus of control beliefs showed the acupuncture patients believed less in the scientific basis of orthodox medicine and more in its harmful effects compared with all other groups. Again, acupuncture patients more than any other group tended to believe in the efficacy of that therapy to 'cure' major, minor, chronic and psychological problems. Beliefs in the efficacy of complementary therapies were associated with a belief in importance of psychological factors in illness and concerns about the harmful effects of orthodox medicine. Results are discussed in terms of three things: differences between lay and professional medical beliefs; the health education implications for this research, and the role of complementary therapies in general practice and health promotion.