A specific and very sensitive method for the determination of 5-hydroxy-tryptophol (5-HTOL) and 5-methoxytryptophol (5-MTOL) in extracts from human cerebrospinal fluid (CSF) involving the use of mass fragmentography and pentafluoropriopionyl derivatives is described. 5-HTOL and 5-MTOL were determined in human CSF of three patients with leukaemia and from nine patients with neurological disorders. The concentration of free 5-HOT in CSF was in the range of 0.1-33 ng/ml and that of 5-MTOL was 0.3-13.9 ng/ml. For the first time the presence of these compounds in human material has been shown. The concentration of these two alcohols in CSF is markedly lower than the concentration of 5-hydroxyindoleacetic acid. These results suggest that human cerebral 5-hydroxytryptamine is preferentially metabolized to 5-HTOL-hydroxyindoleacetic acid rather than to 5-HTOL and 5-MTOL.