In 35 men treated with testosterone undecanoate (TU) at a dosage of 80-200 mg/day, liver function was measured every 6 months for a period of 72 months. None of the parameters changed. In 8 subjects of 50-62 years of age upon starting this type of treatment, urine flow was not found to decrease over the test period of 72 months. Also other signs of benign prostatic hypertrophy were not reported. In 9 subjects for whom TU was the first type of androgen treatment, no signs of gynaecomastia were found during the first 6 months of the therapy or later. These data provide evidence that TU is a reasonably safe form of oral androgen therapy.