A method is described for obtaining lymph from the abdominal thoracic duct of the anesthetized mouse. The average rate of lymph flow was approximately 0.1 ml/hour, or 5.5 ml/hour/kg body weight. The cell content averaged ll,700/mm3, and the total lymphocyte output averaged 1.10 x 106/hour. There was a significant diurnal variation in the lymphocyte output which was greater in the afternoon than in the morning.