We studied the effect of unilateral sympathectomy on rat quadriceps and gastrocnemius muscle concentrations of endogenous dihydroxyphenylalanine (DOPA), dopamine (DA), and norepinephrine (NE) and assessed the relationships between these catecholamines in several rat tissues. Catecholamines were measured by reverse-phase high-performance liquid chromatography with electrochemical detection. Sympathectomy decreased NE and DA concentrations of muscles to approximately 10% of control values, whereas the DOPA concentration tended to increase. Relatively high concentrations of DOPA were found in the gastrointestinal tract, kidney, and spleen. No correlations were obtained between the tissue concentration of DOPA and NE. A DA-to-NE ratio approximately 1% was observed in liver, muscle, pancreas, spleen, and heart, whereas we found exponentially increasing DA values with increasing NE concentration in tissues obtained from stomach, small and large intestine, kidney, and lung. In conclusion, endogenous DOPA in muscle tissue is not located in sympathetic nerve terminals but probably in muscle cells. DA concentrations in the gastrointestinal tract and in the kidneys were greater than could be ascribed to its role as a precursor in the biosynthesis of NE.