The effect of noradrenaline (NA) on the efflux of rubidium (86Rb) from the rat isolated seminal vesicle was studied in the absence and presence of phentolamine and papaverine. Strips of spirally cut seminal vesicles were incubated in radioactive 86Rb (10 microCi.ml-1) for 2 h. Radioactivity was measured using an autogamma spectrometer, and the flux data were expressed in terms of rate constants per minute, of the reactive isotope efflux. A concentration-effect curve for the effect of NA on rat seminal vesicles was constructed, alone and in the presence of phentolamine (1 mumol/l) or papaverine (5 mumol/l). The results showed that NA (10-1,000 mumol/l) produced concentration-dependent contractions in the rat seminal vesicle. These responses were greatly reduced by phentolamine but markedly enhanced by papaverine. NA significantly increased 86Rb efflux from rat seminal vesicles (control rate constant 0.0042 +/- 0.001; test 0.0064 +/- 0.002, means +/- SE; n = 8 rats; p less than 0.001). This increase (52%) occurred within an exposure of 7 +/- 1 min to NA. Phentolamine decreased the NA-induced increase in 86Rb efflux, by 75 +/- 2%, whereas papaverine enhanced it by 86 +/- 5% of the control value. The mechanism of NA-induced increase in 86Rb efflux was not further investigated but was interpreted in terms of an increase in intracellular K+ (here represented by 86Rb), which will leave the cell (efflux) after initial membrane depolarization.