AbstractA series of five consecutive clinical trials were performed in which the neuropeptide desglycinamide‐(Arg8)‐vasopressin (DGAVP) was administered to human subjects suffering from cognitive and memory complaints. The patients selected for the study were carefully screened with the aid of neuropsychological assessment procedures. The trials were conducted according to a structured design in which the variables ‘dose’, ‘route of administration’, ‘treatment schedule’, ‘diagnostic group’, and ‘severity of deficit’ were varied from trial to trial in order to find optimal conditions for the possible expression of a peptide effect. The results indicate a statistically significant effect of DGAVP on word list learning in patients with mild brain trauma, suggesting that learning performance and memory retrieval are improved after peptide treatment in these patients. Patients with more severe brain trauma did not respond to peptide treatment. Some DGAVP effects, e.g. increased speed of memory search, were observed in patients with age‐a