In 60 physically and mentally healthy human subjects, lumbar cerebrospinal fluid was analysed by mass fragmentography for 5-HIAA, HVA and MOPEG. Individuals with a family history of psychiatric morbidity had significantly greater variation in monoamine metabolite concentrations than subjects without such a family history. In subjects with a family history of schizophrenic psychosis 5-HIAA and HVA concentrations were significantly higher than in subjects with depressive disorders within the family. For subjects with deviant 5-HIAA levels the probability of having a psychiatric family history was 2.7 times higher than in subjects with normal values. For HVA and MOPEG similar relationships, but of a lower significance level, were found. The results suggest that the cerebral monoaminergic transmitter amines play critical roles in the pathophysiology of psychotic and depressive disorders with a family disposition. They also indicate a value of monoamine metabolite determination in CSF for the prediction of family vulnerability for psychiatric morbidity in healthy subjects.