In the present experiments, we investigated contractions of guinea-pig vas deferens or seminal vesicle in various kinds of high K+ solution. The vas deferens showed a phasic contraction followed by a tonic one in hyperosmotic 65 mM KCl (hyper-65K+), isosmotic 60 mM or 120 mM KCl solution. However, isosmotic 154 mM KCl (iso-154K+) solution induced a large phasic contraction followed by a gradual relaxation. Applications of the high K+ solutions to the preparation of seminal vesicle showed almost similar results in tension to those of the vas deferens. In the vas deferens or seminal vesicle, an application of hyper-65K+ solution significantly decreased the relative value for the wet weight of the tissue at 120 min, but that of iso-154K+ solution did not affect the wet weight of both the muscles. In the vas deferens, an hyperosmotic addition of sucrose at a concentration of 25 to 100 mM slightly prevented the tension decreased by the iso-154K+ solution and slightly decreased the relative wet weight. In the seminal vesicle, increasing sucrose concentration significantly increased the tension, but decreased the relative wet weight. In both the muscles of vas deferens and seminal vesicle, an addition of pyrvate or oxalacetate (5.5 mM) to the iso-154K+ solution without glucose maintained the muscle tension at a maximal level in the iso-154K+ solution with glucose for 120 min. Further, the tension decrease in both the muscles induced by iso-154K+ solution was also prevented by hyperosmotic application of NaCl. From these results, it is suggested that the tension decrease by high K+, Na+-deficient solution in the vas deferens is mainly caused by an inhibition of glucose utilization by Na+-deficiency in the medium, however, the seminal vesicle is probably due to the cell swelling and partly the inhibition of glucose utilization by it.