Effects of adenosine and adenosine analogues on spontaneous contractility of the human fallopian tube during different phases of the menstrual cycle were studied. In isthmic preparations, a stimulatory effect by L-N6-phenylisopropyladenosine (L-PIA), with preference for adenosine A1-receptors, was seen mainly during the proliferative phase. In ampullary preparations, stimulation by L-PIA was seen both in the secretory and proliferative phases. Adenosine and 2-chloroadenosine exerted similar stimulatory effects. 5'-N-ethylcarboxamide-adenosine (NECA), with selectivity for adenosine A2-receptors, or D-PIA never showed a stimulatory effect. At concentrations above those needed for stimulation, adenosine, 2-chloroadenosine and L-PIA inhibited spontaneous contractions, in common with NECA and D-PIA. Here, NECA was more potent than L-PIA. The D-PIA and L-PIA were equipotent. The inhibition was seen during the whole menstrual cycle. The competitive adenosine antagonist 8-p-sulphophenyltheophylline (PSøT) reversibly antagonized the stimulatory and inhibitory effects elicited by adenosine and the analogues. The PSøT alone could exert a stimulatory or an inhibitory action on spontaneous contractility. We suggest that adenosine can modulate contractile activity in the human fallopian tube via stimulatory A1-and inhibitory A2-receptors. These receptors are located on the smooth muscle cells, and might act via cAMP. The relative receptor dominance may be influenced by cyclic hormonal changes.