The presence of postganglionic adrenergic nerve fibres in the myocardium of human fetuses ranging in gestational age from 9 weeks to 8 months was studied by the method of glyoxilic acid induced fluorescence (GIF). Heart samples were obtained after legal induced interruption of pregnancy, indicated in part of the cases for genetic defects. Identification of adrenergic nerve fibers in the human heart proved possible only in the second half of gestation. This finding supports the assumption of humoral rather than nervous regulation of heart activity in the first half of intrauterine development of the fetus.