In patients with pancreatic cancer deoxyribonuclease I (DNase I) serum levels were compared with those of other known pancreatic enzymes. Serum deoxyribonuclease I, elastase 1, immunoreactive trypsin, amylase and phospholipase A2 were determined in 40 healthy controls, 28 patients with pancreatic cancer, 49 with chronic pancreatitis and 40 with extra-pancreatic diseases. The analysis of variance showed a significant difference among groups for serum DNase I values. However, none of the 3 groups of patients had a mean deoxyribonuclease I value higher than that of the healthy controls. In pancreatic cancer and chronic pancreatitis patients, increases in the 4 pancreatic enzymes values were found in percentages that were higher than those for DNase I. A significant correlation was found between DNase I and phospholipase A2, but not between DNase I and elastase 1, immunoreactive trypsin and amylase serum activities. The findings indicate that deoxyribonuclease I serum determination is an even less satisfactory index of pancreatic malignancy than the other pancreatic enzymes. Rather than expressing pancreatic damage, any variations in this enzyme appear more likely to reflect an aspecific phenomenon.