The authors studied the effect of pyruvate and oleate on O2 consumption of the frog sartorius and heart ventricle. 10 mM pyruvate raised O2 consumption of both tissues by over 100%, but only in the winter. Raised O2 consumption was only partly associated with glycogen synthesis from pyruvate. 0.1 mM oleate reduced O2 consumption in both tissues. A marked drop in O2 consumption was observed in the ventricle (up to 50%). Lecithin had a similar effect on O2 consumption. The addition of pyruvate plus oleate led to an 8-fold increase in O2 consumption of the ventricle, i.e. to maximum oxidation capacity of the tissue, but the addition of lecithin inhibited the pyruvate-induced increase in O2 consumption. It is assumed that both pyruvate and oleate influence resting metabolism in a specific manner which cannot be attributed solely to raised availability of substrate for resting energy metabolism requirements.