Astrocytes transport the monocarboxylate acetate, but synaptosomes do not. The reason for this is unknown, because both preparations express monocarboxylate transporters (MCT). The transport and metabolism of lactate, another monocarboxylate, was examined in these two preparations, and the results were compared to those for acetate. Lactate transport is more rapid in astrocytes than in synaptosomes, but of lower affinity (K_ms of 17 and 4 mM, respectively). Lactate (0.2 mM) is metabolized to CO₂ more rapidly in synaptosomes than in astrocytes (rates of 0.37 and 0.07 nmol · mg protein⁻¹ · min⁻¹, respectively). The reason for this is unclear, but cellular differences in lactate dehydrogenase isotype expression may be involved. Acetate is metabolized to CO₂ more rapidly in astrocytes than in synaptosomes (rates of 0.43 and 0.02 nmol · mg protein⁻¹ · min⁻¹, respectively). This is likely due to cellular differences in the expression of monocarboxylate transporter subtypes.