Résumé : Testosterone undecanoate (TU) or placebo was administered orally (for 12 weeks) in a double blind study, to 19 patients with chronic renal insufficiency on hemodialysis in a daily dose of 240 mg. Effect on plasma testosterone (T), dihydrotestosterone (DHT), androstenedione (A), 110H androstenedione (110A), FSH, LH and PRL concentration and the pituitary responsiveness to LH-RH/TRH stimulation was studied. These hormone levels were determined before the study and after 6 and 12 weeks of treatment. There was a rise in plasma androgen concentration in all treated patients. Mean plasma DHT, A and 110A increased at 12 weeks from 0.3, 0.85 and 1.13 ng/ml to 1.13 (p less than 0.05), 1.4 (p less than 0.05) and 1.44 (p less than 0.05) respectively. There was no change in plasma T or free testosterone. However, basal LH, FSH fell progressively from 5.51 and 5.51 ng/ml to 2.13 and 1.84 ng/ml (p less than 0.05). The level of significance of these changes was confirmed when the response to LH-RH was considered. Basal plasma PRL also decreased from 376 microU/nl to 306 (p less than 0.05), but PRL response to TRH remained unchanged. In contrast, none of these modifications were observed in placebo-treated patients. We conclude that oral TU restored to normal the pituitary-testicular axis. This form of treatment should be preferentially chosen instead of intramuscular injections in these frequently heparinized patients on hemodialysis.