A study of the effects of discontinuing or reducing maintenance medication in chronic schizophrenic men provided an opportunity to evaluate the clinical usefulness of one of the rapid semi-quantitative urine tests (FPN). The rate of excretion of chlorpromazine and thioridazine after placebos had been substituted was determined and the effects of intermittent administration of drugs were observed. The FPN test performed as expected, also providing some interesting information about patients' drug taking behavior. The lower colorimetric readings obtained with thioridazine were most interesting but do not preclude the use of the test done with strict attention to detail in a clinical setting. As the FPN test is a qualitative procedure, its semi-quantitative potential as used in this study should be considered an approximation yielding usable comparative results.Abstract Teaser