The frequency and degree of elevated serum levels of trypsin (T) and correlation with other pancreatic enzymes were determined in several groups of patients with renal disease, i.e., patients with chronic renal failure (CRF), hemodialysis patients (HD), renal transplant recipients (RT), and in a control (C) group. Mean values of T were significantly higher in all other groups than in the C group (p less than 0.0001). A statistically significant correlation between T and creatininemia levels was found only for the RT group (p less than 0.0001). Correlations between T versus pancreatic amylase and T versus lipase activity were found to be statistically significant in the CRF and RT groups (p less than 0.01), but not in the HD group. Most patients in all groups had T values higher than the maximum value observed in the controls and, of them, most had very elevated values. The results suggest that in chronic renal pathology there are frequent and significant increases in serum T levels, circulating in parallel with the other pancreatic enzymes. It is possible that, together with the renal excretion impairment, there could also be subclinical pancreatic damage or a dysfunction of the other means of elimination of T that can be responsible for, or contribute to, the serum increase in the enzyme.