Endocrine and metabolic features were studied in two patients with xeroderma pigmentosum. Consistent findings included a nonspecific aminoaciduria of the overflow type involving aspartic and glutamic acid, reduced creatinine clearance, low urinary steroid excretion with subnormal responses to adrenocorticotrophic hormone (ACTH), and metyrapone stimulation. Baseline plasma cortisol and the response to ACTH were normal. Erythrocyte glucose-6-phosphate dehydrogenase (G-6-PD) activity was slightly prolonged. No abnormalities were found in the serum α2-globulins, ceruloplasmin, serum copper, or transaminase (SGOT) levels. The presence of a generalized metabolic disorder involving the skin, kidney, and liver is considered.