Serum luteinizing hormone (LH) levels were determined every 15 minutes, between 6:00 a. m. and 6:00 p. m., in four normally active men. Each subject demonstrated a repetitive pattern of abrupt elevations throughout the day. Twenty-one elevations were found during the total of 48 hours of monitoring. In the four volunteers, ratios of the highest to lowest levels of gonadotropin during the 12 hours ranged from 2.1–2.9. Individual or averaged concentrations of LH may not completely characterize pituitary-gonadal relationships.