Six patients with advanced prostatic cancer who had been treated by long-term administration of LH-RH agonistic preparations (Buserelin or Leupron) were tested for their pituitary-testicular endocrine functions. Serum levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone (T), prolactin (PRL), estradiol (E₂) and dihydrotestosterone (DHT) were measured consecutively. In all medically castrated patients, serum levels of LH, FSH, T, DHT anbd E₂ were suppressed and particularly serum T levels were below the castration level of 1.0ng/ml. On the other hand, serum PRL levels were unchanged after the long-term treatment with the agonists. Serum LH and FSH levels failed to respond to LH-RH stimulation after the treatment, whereas serum T responded to stimulation by human chorionic gonadotropin (hCG) to various degrees. It was remarkable that, in 4 out of 6 medically castrated patiejnts treated up to more than 3 years, serum T response levels above 1.0ng/ml were noted. It is suggested that testicular endocrine function to secrete T and DHT in patients under treatment with long-term LH-RH agonist administration are still preserved in response to hCG stimulation.