The response of luteinizing hormone to a single injection of synthetic LRH was established in 6 women and 7 men following an intramuscular dose of 0.2mg or 0.1mg. Significant increases of serum LH were observed in 30 min. Pretreatment with metyrapone for one day (4.5 g/sugject injection of synthetic LRH (0.1 MG/SUBJECT). Seven women, 21-48 years of age who were treated with prednisolone for a least 11/2 months were examined for responsiveness of the anterior pituitary to a single injection of synthetic LRH (0.2 MG). The secretion of LH was markedly suppressed and maximal serum levels of LH WERE OBSERVED 90 MIN FOLLOWING LRH injection.