The aim of this study was to evaluate, in renal transplant recipients with different function of the graft, the urinary excretion of some low molecular weight proteins and tubular enzymes frequently employed as indicators of tubular dysfunction. Urinary excretion of proteins and enzymes was measured in 51 renal transplant patients and, for comparison, in 73 patients affected by different kidney diseases with various degrees of renal function. Values of urinary beta 2-microglobulin and retinol-binding protein higher than normal were found in most transplanted patients, even in those with good renal function. On the other hand, in renal patients the urinary excretion of low molecular weight proteins was high only when creatinine clearance was lower than 30 mL/min/1.73 m2. Furthermore, an increased urinary excretion of tubular enzymes was found in a higher number of transplanted patients than of renal patients. This behavior was particularly evident for lysosomal enzyme N-acetyl-beta-D-glucosaminidase. In conclusion, a tubular dysfunction occurs in the transplanted kidneys, even in those with well preserved glomerular function.