Measurements of the O2 consumption and of the potential of frog skin, made under comparable conditions, show that the homologous carbamates (ethyl, propyl, butyl, and amyl) reduce both the O2 consumption and the potential, but not in a similar manner. In this respect, the effect of the carbamates is like the effect of reduction in O2 tension. The simple lysins (saponin and the bile salts), on the other hand, abolish the potential without reducing the O2 consumption at all. Irrespective of whether one considers the concentration of carbamate in the entire system or the amount of carbamate adsorbed by the frog skin, Traube's rule relating the effect of a carbamate to its position in the homologous series does not seem to apply.