The effects of iodoacetic acid (IAA), IAA and 2,4-dinitrophenol (DNP), and ethacrynic acid (ETCA) (each 10−3 M) on Na, K, Ca, and water movements in rat uterus were studied. All these compounds caused tissues to gain Na, Ca, and water and lose K. The ratio of K loss to Na gain was much lower with ETCA as compared with IAA or IAA and DNP. Net Ca movements showed a definite lag compared with those of Na and K in every case. The gain in tissue water after IAA or IAA and DNP was greater than that after ETCA, which also occurred much later. The loss of K except with ETCA was initially greater than the Na and Ca gained in exchange for it. Subsequently in IAA or IAA and DNP the Na and Ca gained, unaccompanied by bathing solution, was in excess of K loss, as it was from the beginning with ETCA. These results suggested a different metabolic dependence and (or) a different transport mechanism controlling Ca distribution from that controlling Na and K distribution. Furthermore, the mechanism controlling H2O distribution seems to be partially independent of net sodium gain. The data also suggest that binding and unbinding of cations may be involved in controlling ion distribution in the rat uterus.