Biochemical prevalence in suicidal behavior was investigated by evaluating 61 patients with or without repeated suicidal behaviour before or the year after an index attempt. Lumbar punctures were performed after a mean wash-out period of 16 days after admission, & complete cerebrospinal fluid & urinary biochemical data were available for all subjects. Clusters of clinical & biochemical variables proved to be the best predictors of suicide. (30 refs.)