Pharmacokinetic parameters of methadone were studied in adult dairy goats. Five goats were each given methadone hydrochloride as a single 0.2 mg/kg of body weight dosage by intramuscular (IM) administration. Plasma methadone concentrations were determined for 96 h after dosing. Plasma methadone concentrations after IM administration were best described by an open one-compartment model. Overall elimination half-life (t1/2) was 1.38 h. Peak plasma concentrations were reached 0.25 h after dosing, and the actual plasma concentration averaged 37.8 ng/ml (SD = 12.76) at that time. The data obtained from this study suggest that plasma concentrations, similar to those that are analgesic in humans, can be achieved after IM administration of methadone at a dose rate of 0.2 mg/kg of body weight. In addition, these plasma concentrations can be maintained for up to 3 h after a single injection and, therefore, may provide satisfactory analgesia for such period.