In 36 drug-free schizophrenic patients, lumbar CSF was analyzed by mass fragmentography for the major monoaminergic transmitter metabolites 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid (HVA), and 3-methoxy-4-hydroxyphenylglycol (MHPG). High or deviant concentrations of 5-HIAA were significantly related to a family history of schizophrenia. For patients with deviant 5-HIAA levels, the probability for a family history of schizophrenia was eight times higher than in subjects with normal values. High concentrations of HVA also tended to be significantly related to a family history of schizoprenia. The majority of schizophrenic patients, who lacked family history for the disorder, had normal monoamine metabolite concentrations in CSF. The results suggest a coupling between biochemical variables related to central serotonin and dopamine metabolism and forms of schizophrenia that have a familial disposition.