The effects of furosemide, ethacrynic acid, triamterene, and an aldosterone antagonist (Su-11927) were studied on recovery of electrolyte gradients by Na-rich pieces from rabbit uteri and aortas. In sufficient concentration furosemide and ethacrynic acid appeared to inhibit Na extrusion. Only furosemide inhibited K uptake as well. A small concentration of ethacrynic acid (0.1 μg/ml) increased Na extrusion from Na-rich uterine pieces but did not increase K uptake. Thus K gain and Na extrusion were not always reciprocally related. Triamterene and Su-11927 altered recovery of electrolyte gradients, but convincing evidence for inhibition of Na active transport was not obtained. Whether inhibition of Na extrusion without inhibition of K uptake, as by ethacrynic acid, could be considered convincing evidence of inhibition of active transport was discussed.