The development of the germinal and somatic cells in the gonads of normal and anencephalic fetuses was investigated. Interstitial cells were reduced in number in both sexes and in males the population of gonocytes in profiles of seminiferous tubules was reduced when Leydig cells were seeminaly absent. Ovarian differentiation up to about 34 weeks after conception was apparently normal, although precise counts of the numbers of germ cells were not carried out. Nevertheless, oogonia increased in number by mitotic divisions, oocytes progressed through meiotic prophase to the diplotene stage, and primordial follicles formed normally. By contrast, 'growing' and small antral follicles, which are a constant feature of control ovaries, were not observed in the anencephalic specimens.