In 1941 Huggins and Hodges demonstrated that castration slowed progression of prostate cancer. Treatment with a luteinizing hormone releasing hormone (LHRH) agonist is a standard alternative to surgical castration for patients with prostate cancer and metastases. We evaluated patients with prostate cancer undergoing long-acting LH-RH agonist hormone therapy to determine the length of time that serum testosterone remains at castration level. Between June 2007 and October 2009, we studied 73 patients treated with LH-RH agonist. Castrate serum testosterone was defined at 50 ng/dl and less. The interval of administration of LH-RH agonist was extended to 5 months, and the testosterone level was measured. The testosterone level was 50 or less in almost all patients at 5 months after long-acting LH-RH therapy. The ratio of patients to whom dosing of LH-RH agonist was terminated who have a testosterone level of 50 ng/dl and lower was at 100% to month 7 and 7% to months 10 -19. We believe that therapy whereby long-acting LH-RH agonist is dosed may be extended to 5 to 7 months if male hormone values are monitored. Our data suggest that using serum testosterone to guide LH-RH hormone dosing is efficacious and cost-effective.