A simple method is described for the simultaneous determination of the three monoamine metabolites, 4-hydroxy-3-methoxyphenylacetic acid, 4-hydroxy-3-methoxyphenylethyleneglycol and 5-hydroxyindole-3-acetic acid, in cerebrospinal fluid by high-performance liquid chromatography with electrochemical detection. Quantitation is accomplished by the standard addition technique. Chromatographic peak heights are corrected for volume effects by comparison with the signal obtained for an added auxiliary reference substance. Sample preparation is kept to a minimum, involving precipitation of proteins by means of perchloric acid and subsequent neutralization. The reproducibility was estimated to be 10%. For one of the metabolites, 4-hydroxy-3-methoxyphenylethyleneglycol, a correlation between the results obtained by this method and a mass fragmentographic method was made, and a satisfactory correlation (r = 0.904, slope = 0.914, intercept 3.26 ng/ml) found. The sensitivity of the method is in the picogram range. The methodology has been applied to measure biogenic amine metabolites in both rabbit and human cerebrospinal fluid. The levels found are in agreement with previously reported values.