Plasma values of immunoreactive interleukin-6, C-reactive protein and phospholipase A have been determined in serial samples from 24 patients with acute pancreatitis ('mild' pancreatitis nine, 'severe' pancreatitis 15). Median plasma concentrations of interleukin-6, C-reactive protein, and phospholipase A activity were significantly higher in patients with 'severe' illness (p < 0.001) than those with 'mild' illness. A particularly marked increase in interleukin-6 was found in two patients with necrotising pancreatitis and fatal outcome. Significant correlations between plasma concentrations of interleukin-6 and phospholipase A (p = 0.0218) and C-reactive protein and phospholipase A activity (p < 0.0001) were found in patients with 'severe' disease. These findings in a limited number of patients with acute pancreatitis are promising in that raised interleukin-6 correlated with clinical severity and with two other established markers, C-reactive protein, and phospholipase A activity.