The effects of gamma-aminobutyric acid (GABA) and some GABA ergic compounds were examined on the spontaneous contractile activity of the ampullar segment of human Fallopian tubes in vitro. In both circular and longitudinal smooth muscle layers, GABA increased the frequency, and decreased the amplitude of the contractions. In longitudinal muscle layer, this effect occurred independently of endocrine status, while in the circular muscle layer, the amplitude was affected only in follicular phase and in postmenopause, but not in the luteal phase. Baclofen mimicked the effects of GABA, whereas muscimol and bicuculline failed to influence the contractility. Our findings suggest that, in the ampulla of the human oviduct, GABAB-receptors may be involved in the regulation of motility, and thus in the modulation of ovum transport and fertility.