The concentrations of glutamine and other amino acids were measured in plasma and intracellular fluid of soleus and extensor digitorum longus (EDL) muscles of rats 4, 8, and 16 hr after induction of sepsis by cecal ligation and puncture or after sham operation. Previous studies have shown that muscle protein breakdown is greatly increased in EDL, but not in soleus muscle, in this sepsis model. Corresponding to previous observations of protein breakdown in sepsis, muscle glutamine was markedly depleted (< 50%) in EDL by sepsis, while no significant fall in glutamine concentration in soleus was observed. Changes in muscle glutamine concentration in sepsis could not be attributed to changes in the precursor of glutamine, glutamic acid. Data were examined for changes consistent with hypothesized alterations in glutamine transport. Correlations among glutamine and other amino acids in muscle, histidine in particular, were consistent with a sepsis-induced alteration in activity of the sarcolemmal glutamine transporter, system Nm. These results thus strengthen the proposed connection between muscle glutamine content and muscle protein metabolism under catabolic conditions.