Robert Buckman, a medical oncologist, and George Lewith, a homoeopathic physician, met in Southampton while filming ''Magic or Medicine?,'' a television series of four programmes about what can and might be learnt from the popularity of complementary medicine. In particular, the series showed how the effect of the patient's and the doctor's beliefs affected the relationship between them. The two doctors so enjoyed talking with each other that they carried on their debate in letters to each other over the next year. We think that their exchange merits a wider readership.