Levels of urine and serum lysozyme are elevated in patients whose C<sub>Cr</sub> is below 30 ml/min. In nine patients undergoing maintenance hemodialysis the mean urine and serum lysozyme concentrations were 29.6 and 21.9 µg/ml, respectively, and remained constant with dialysis. In five patients on peritoneal dialysis the mean predialysis urine and serum lysozyme concentrations were 14.9 and 18.5 µg/ml, respectively. An average 17% fall of serum lysozyme concentration was observed post peritoneal dialysis – consistent with protein loss across the peritoneal membrane. Lysozyme in the presence of urine was shown to inhibit bacterial growth of P. mirabilis, E. coli and Pseudomonas sp. Lysozymuria in conjunction with other elements of urine may account for the only moderately increased prevalence of bacteriuria (10<sup>5</sup> col/ml) observed in nondialyzed azotemic patients (22%) and uremic patients supported by hemodialysis (24%).