AbstractNa‐metavanadate and ouabain that act on Na+K+‐ATPase had no influence on insulin binding toTetrahymenaimmediately after treatment, but after 24 h considerably enhanced the binding capacity of generations of progeny. The increase in binding was of a similar magnitude to that elicited by insulin imprinting. Vanadate failed to increase the imprinting potential of insulin while ouabain even prevented insulin imprinting when administered together with insulin, but, did not affect imprinting when administered after insulin. By analogy with higher organisms it appears that inhibition of Na+K+‐ATPase plays no role in the insulin‐like effect of vanadate on the unicellularTetrahymena, as judged also from the capacity to bind insulin of the generations of of