The metabolites of serotonin, dopamine, and norepinephrine, 5-hydroxyindoleacetic acid (5HIAA), homovanillic acid (HVA), and 3-methoxy-4-hydroxy-phenylethylene glycol (MHPG), respectively, were studied in cerebrospinal fluid of patients with acute schizophrenia. Base line levels of these metabolites were not significantly different from those in normal, neurological, and affectively ill controls. Accumulations of 5HIAA and HVA following probenecid administration, which provide a measure of serotonin and dopamine turnover, were also not significantly different in patients with acute schizophrenia and affective illness. After patients had recovered from their acute schizophrenic illness, HVA accumulations were significantly reduced. We discuss results in relation to amine hypotheses of schizophrenia and the suggestion that altered dopamine metabolism may reflect a biological change predisposing to acute schizophrenia.