In the present study, we found that large quantities of dopamine (DA) glucuronide were present in rat cerebrospinal fluid (CSF), plasma, and urine, whereas the glucuronides of norepinephrine (NE) and epinephrine (E) were almost undetectable. The high urinary excretion of DA glucuronide was in a range comparable to that of homovanillic acid (HVA). Sulfates of DA, NE, and E were measurable in all three body fluids, but only in small quantities. The measured DA glucuronide was predominantly of endogenous origin, as the feeding of sucrose instead of routine diet did not reduce the urinary output of DA glucuronide. Adrenalectomy but not peripheral sympathectomy induced by chronic guanethidine injection substantially decreased plasma DA glucuronide concentrations, indicating that the adrenals serve as an important source of endogenous DA glucuronide. The data suggest that glucuronidation constitutes an important metabolic pathway for endogenous DA of central and peripheral origin in rats; this route, however, is exclusive to DA and appears to play a negligible role for NE and E.