Dietary zinc intake was restricted (2.7 to 5.0 mg daily) for 24 to 40 weeks in five male volunteers. Their mean age was 57 years. Oligospermia (total sperm count less than 40 million per ejaculate) was induced in four out of five subjects. A decrease in the sperm count occurred during zinc restricion and the early phase of zinc repletion before body stores of zinc were restored to normal. The duration of oligospermia in the four subjects ranged from 6 to 14 months. Oligospermia was reversed after zinc supplementation in physiologic amounts. The baseline sperm concentration and total sperm count per ejaculate in all five subjects dropped significantly (p < 0.05) after zinc restriction and returned to normal 6 to 12 months after zinc supplementation. The decrease in sperm count coincided with decline in Leydig cell function and was reversed after zinc supplementation in low doses. Our study has demonstrated that dietary restriction of zinc can affect testicular function adversely. This effect of zinc deficiency, however, is a reversible process and can be corrected by proper supplementation with zinc.