Plasma and urinary concentrations of amino acids were investigated during diabetic ketoacidosis (DKA) and 12, 24, 72 hours after initiation of therapy. In DKA plasma concentration of glutamic acid, asparaginic acid, valine, leucine and isoleucine significantly increased while that of asparagine and glutamine decreased compared to levels in well controlled diabetic patients. Despite the elevated urinary excretion of branched chain amino acids, histidine, serine and threonine, urinary excretion and clearance of glutamic acid, glutamine, glycine and taurine were reduced. Among the different amino acids histidine excretion had the highest variability. Strong correlation was found between the urinary excretion of several amino acids and that of the beta-2-microglobulin characterizing tubular dysfunction. Changes in the excretion of different amino acids reflect the altered metabolic state and renal function due to diabetic ketoacidosis.