A simple procedure is described, suitable for large scale preparation of ovine luteinizing hormone (LH, ICSH) having high biological activity. The method has been routinely employed in preparation of ovine luteinizing hormone of the NIH-LH series for the Endocrinology Study Section. Preparations both equipotent with and 2 times as potent as the NIH-LH-S1 standard may be obtained in good yield by the methods described. Based on the ovarian ascorbic acid depletion assay of Parlow, a critical analysis, and comparison of LH preparations obtained by the methods reported here with those prepared by various other procedures, suggest that they are at least equal in potency to any reported previously. Attempts at further purification by molecular sieving on columns of the dextran gel, Sephadex G-100, are also described. These experiments suggest that LH preparations having a specific activity significantly greater than those described above are attainable.