Physiological and pharmacological characteristics of the spontaneous motility of rat oviductal tracts (the coiled oviduct plus its mesosalpinx), isolated in proestrus, estrus or metestrus, are described. The initial contractile tension (recorded following isolation) was comparable in the three stages of the cycle, but its decrement with time was greater in metestrus than in proestrus; the opposite being observed regarding the rate of contractions. Norepinephrine and phenylephrine depress motility in proestrus and metestrus, but not in estrus. The inhibition of motility during proestrus, produced by added norepinephrine, phenylephrine or isoproterenol was not modified by phenotolamine but was abolished by propranolol. During estrus, norepinephrine and phenylephrine inhibited tubal contractions of preparations incubated with phentolamine, whereas it produced a distinct stimulation in the presence of propranolol. It is concluded that: (a) the rat mesosalpinx might play some role in the motility of the whole isolated oviductal tract; (b) there are variations in the decrement with time of contractile tension and frequency of contractions in different stages of the sex cycle; (c) the effects of catecholamines upon the rat oviductal tract also varies within the cycle, probably due to influences imposed by sex hormones.