Na⁺, K⁺-ATPase is a component of plasma membrane in almost all animal cell, and maintains ionic distribution and membrane potential of normal cell. In the mechanism of adrenergic transmission, it is relatively well known that drug-receptor combination leads to stimulate adenylate cyclase and so on. In the cholinergic transmisison, the mechanism is not well known but is simply interpreted as the change of membrane permeability results from acetylcholine receptor interaction. To study the relationship between cholinergic transmission and membrane Na⁺, K⁺-ATPase, the effect of carbachol on Na⁺, K⁺-ATPase activity in rabbit erythrocyte membrane is studied. The results are summarized as follows. 1) Total ATPase, Mg²⁺-ATPase and Na⁺, K⁺-ATPase of rabbit erythrocyte membrane show maximum activities at 1mM of tris-ATP. 2) Total ATPase activity tends to increase when treated with carbachol (10-^-9M-10^-3M). 3) The Mg²⁺-ATPase activity also tends to increase when treated with carbachol (10-^-9M-10^-3M). 4) The Na⁺, K⁺-ATPase activity is inhibited when treated with carbachol (10-^-9M-10^-7M). It is suggested that the inhibition of Na⁺, K⁺-ATPase by cholinergic drugs may be considered as one part of mechanism of cholinergic transmission.