To gain some insight into the process by which both acetylCoA and NADPH, needed for fatty acid synthesis, are obtained, in the cytosol, from the effluxed intramitochondrial citrate, via citrate lyase and malate dehydrogenase plus malic enzyme respectively, the capability of externally added pyruvate to cause efflux of malate from rat liver mitochondria was tested. The occurrence of a pyruvate/malate translocator is here shown: pyruvate/malate exchange shows saturation features (Km and Vmax values, measured at 20 degrees C and at pH 7.20, were found to be about 0.25 mM and 2.7 nmoles/min x mg mitochondrial protein, respectively) and is inhibited by certain impermeable compounds. This carrier, together with the previously reported tricarboxylate and oxodicarboxylate translocators proved to allow for citrate and oxaloacetate efflux due to externally added pyruvate.