SUMMARY The assay method for luteinizing hormone (LH) activity depending on ovarian ascorbic acid depletion in rats (O.A.A.D. method) has been assessed in terms of its reliability criteria. The chief advantages of the method are its high degree of sensitivity and specificity and its good practicability. Its disadvantages are its relatively low degree of precision and the fact that a proportion of assays are invalid due to lack of parallelism. The LH activity of various gonadotrophin preparations has been investigated using the O.A.A.D. method. The LH content of NIH-FSH and of Pergonal was found to be low. The LH activity of pregnant mare's serum gonadotrophin was lower than that of human chorionic gonadotrophin. When purified urinary extracts are used, the O.A.A.D. method is suitable for clinical application.