Early diagnosis of threatening renal complication is essential for the adequate treatment of acute pancreatitis. Deposition of phospholipase A2 (PLA2) in rat renal proximal tubular cells has been observed in experimentally induced acute pancreatitis. The value of measuring the catalytic activity of PLA2 in serum as an early warning of developing renal tubular cell injury was therefore investigated in a prospective study of 31 consecutive patients suffering from acute pancreatitis. A positive correlation was found (r = 0.66, P < 0.001) between the highest serum PLA2 activity, as measured early in the course of acute pancreatitis, and the highest N-acetyl-beta-glucosaminidase (NAG):creatinine ratio in the urine. The correlation between the highest serum concentration of immunoreactive pancreatic PLA2 and the highest urinary NAG:creatinine ratio was weaker (r = 0.36, P < 0.05). These results indicate that the measurement of the catalytic activity of PLA2 in serum early in acute pancreatitis may provide a simple test for the detection of threatening renal complication.