Urinary steroid hormone content was determined in Black and White North American men and in rural Black South African men between 40 and 55 years of age and in Black South African men over 60 years of age when maintained on their customary diets or when transferred to a vegetarian or Western diet, respectively. When eating their customary diets, Black South African men had lower levels of urinary estrogens and androgens than did Black and White North American men. The total androgen content decreased significantly in Black North American men on the vegetarian diet and increased in Black South African men fed a Western diet. Urinary excretion of estrogens was higher in older than in younger rural Black South African men. Data indicated that a vegetarian diet modified androgen and estrogen metabolism in North American men and that a Western diet was associated with higher levels of urinary steroid hormones in young Black South African men. Diet-related changes in steroid metabolism in rural Black South African men were age dependent. The relationship of the increased urinary excretion of steroid hormones in Black South African men, a low-risk group fed a Western diet, and the decreased excretion in Black and White North American men, high-risk groups fed a vegetarian diet, to the development of prostatic cancer remains to be clarified.