The last thirty years have witnessed intense activity in the field of clinical psychopharmacology, since the birth of contemporary psychopharmacology in Paris in 1952 with the production and clinical evaluation of chlorpromazine. That original evaluation of chlor-promazine was relatively straightforward (Delay & Deniker, 1952). Its efficacy in controlling psychotic manifestations was so clearly superior to existing means at that time that no subtle clinical rating scale or statistical device was required to throw the observed benefit into relief. Since that time there have been many developments in the field of psychopharmacology and several new families of anti-schizophrenic drugs have appeared. During this process certain rules of clinical assessment have evolved and have become incorporated into a research and development ritual which now tends to be applied to any new anti-schizophrenic candidate. There is no doubt that real evolution has taken place in the technology of clinical assessment and that experimenters are more aware of the basic requirements needed to arrive at some scientific conclusion.