Endocrine parameters were assayed in a San ("Bushman") population of Botswana in an attempt to correlate hormonal secretion and body morphology. Serum levels of gonadotrophins and gonadal steroids were measured by employing radioimmune methods. No evidence for elevated estrogens could be found and males showed endocrine levels comparable with European and South African Negro values. Females have suppressed circulating levels of gonadal steroids and little corpus luteum function. A mechanism by which the ovaries may be suppressed, thereby limiting conception to times of high nutrition, may exist in the San. This hypothesis may have a bearing on the observation that births reach peak levels during March and April.