The present study aims to explore the effects of the phosphodiesterase inhibitors tadalafil and vardenafil on the spontaneous contractions of isolated rat myometrium. The study included 45 virgin female rats weighing between 250 and 260 g. Two different agents were used in two different tissue cross-sections taken from each animal. Spontaneous contractions as well as the contractions following tadalafil and vardenafil applications (200, 400, and 600 mu l) in the tissue preparations, were evaluated in 10 minute periods in terms of frequency, amplitude, and the area under the contraction curve. Isometric contractions were measured and evaluated on the oscillographic records. The highest tadalafil dose (600 mu l) significantly reduced frequency in comparison to control values (p<0.01). Vardenafil did not produce any effect on contraction frequency. When the effects of the agents on contraction amplitude were evaluated, the highest dose of tadalafil was again found to lead to a significant drop in the amplitude (p<0.05). The same dose of tadalafil was also seen to markedly decrease the area under the curve (p<0.05). Results of the study indicate that tadalafil markedly inhibits the frequency, amplitude, and area under the contraction curve, all of which are isolated myometrial contraction parameters in rats, in a dose-dependent manner. However, vardenafil did not produce any effect on these parameters.