Random urine samples were obtained to evaluate potential age- or urine concentration-related differences in lysozyme or NAG content. The concentration and excretion of both enzymes was widely variable although no age-related differences were seen. Urine concentration, however, was an important variable as NAG concentration (per mL urine) and lysozyme excretion (per mumol creatinine) were significantly elevated and reduced, respectively, in samples with a higher specific gravity. The correlation coefficient between urine specific gravity and both parameters was significant. Lysozyme excretion is elevated in subjects undergoing a modest diuresis although NAG excretion is unaffected. These data may prove to be useful in the evaluation of renal dysfunction.