The effect of xylazine hydrochloride on biochemical and endocrine parameters in plasma was examined in adult white-tailed deer (Odocoileus virginianus (Zimmermann]. In the first experiment, seven animals were injected intramuscularly via a blowgun dart with 0.65 mg/kg xylazine (100 mg/ml) and were bled 10, 20, 30, and 60 min post-injection. In the second experiment, eight animals were manually restrained for the first blood sampling and then injected manually and bled as before. Plasma calcium (Ca), inorganic phosphorus (P), and alkaline phosphatase (AP) were measured spectrophotometrically. Plasma parathyroid hormone (PTH), calcitonin (CT), thyroxine (T4), triiodothyronine (T3), and cortisol were measured by radioimmunoassay. Plasma PTH, CT, T4, T3, and AP activity did not differ (P greater than 0.05) during the 1 hr period studied in either experiment. Plasma Ca and P decreased significantly (P less than 0.05) in the second experiment, whereas cortisol levels increased significantly (P less than 0.05) 10 min post-injection in both experiments. The results may have been due to a drug effect or a combined drug and stress effect. It is suggested that xylazine may be safely used as an anesthetic in measuring PTH, CT, T4 and T3, and plasma AP up to 60 min post-injection in deer. Caution should be taken in using xylazine as an anesthetic to study adrenocortical function.