The urinary excretion of biopterin and neopterin, pterin compounds related to tetrahydrobiopterin, the cofactor for the initial steps in monoamine synthesis, was serially measured in a heterogeneous group of psychiatric patients and compared to excretion in control subjects, to state of illness, and to the results of the dexamethasone suppression test. Patients with major depression had increased excretion of biopterin compared to normal subjects. There was no relationship between biopterin or neopterin excretion and postdexamethasone cortisol levels. Pterin excretion did not significantly change with improvement in mood or with conversion from nonsuppressor to suppressor status. The meaning of increased urinary biopterin is presently unclear, although its relation to hormonal state and sympathoadrenal tone deserves further study.