We describe a mass-fragmentographic method for determination in urine of the following metabolites of L-3,4-dihydroxyphenylalanine and dopamine: vanillactic acid, 3,4-dihydroxyphenylacetic acid, 3-methoxy-4-hydroxyphenylethanol, and 3,4-dihydroxyphenylethanol. Deuterated analogs were used as internal standards. The method is fast, reproducible, sensitive, and selective, and does not require the use of time-consuming clean-up procedures. Normal excretion values in terms of creatinine, expressed as a function of age, as well as values obtained for patients with neurogenic tumors, a patient during therapy with L-3,4-dihydroxyphenylalanine, and a patient receiving dopamine are presented and discussed.