In a previous study (Willcox et al., 1965), we reported the results of urine tests on a series of psychiatric out-patients, done with the aim of determining whether the patients were taking their pills as prescribed. We now report a similar study on in-patients. It is a matter of clinical experience that some psychiatric in-patients avoid taking their pills as prescribed, for in-patients who take an overdose in a suicidal gesture often say that they 'saved up’ their prescribed pills in order to do this. There are many other reasons, such as the occurrence of unpleasant side-effects or a belief that the pills are not doing any good, which might lead in-patients to avoid swallowing their pills at medicine-time, and though we should not expect to find this happening as often in in-patients as in out-patients yet the proportion of cases in which this occurs and whether it occurs more often with one type of drug than another are matters of general concern.