PIP: The promotion of sexual maturity in a genitally hypoplastic adult ma le by testosterone propionate (TP) is reported. TP was injected 3 times a week in a dose of 5 mg for about 4 months. The dosage was then increased to 25 mg, 3 times a week. Almost 7 months after the start of treatment, genital size had increased, and live spermatozoa were evident in the ejaculate. The voice became somewhat deeper, but the initial beardlessness and distribution of hair was unchanged. In laboratory studies with TP, stimulation and proliferation of the germinal epithelium was apparent, but maturation of the testes was not accelerated. In the case reported, it is concluded that the increase in dosage caused proliferation of spermatozoa after stimulation of germinal epithelium maturation.