To determine whether or not phosphorylation of skeletal muscle proteins is related to functional specialization of individual muscles, we examined the distribution of phosphoproteins in skeletal muscles with different functional properties. Protein phosphorylation was carried out using [γ-32P]ATP and employing endogenous protein kinases present in skeletal muscle homogenates. Phosphoprotein bands were separated by polyacrylamide gel electrophoresis. We found distinct cAMP-stimulated and basal phosphoprotein patterns in each contraction type; indicating that the phosphoprotein profile is related to functional characteristics. Muscle-specific, cAMP-dependent phosphoproteins may permit coordinate short-term alterations in twitch characteristics of skeletal muscle fibers in response to circulating hormones or other mediators.