Interleukin-6 (hepatocyte stimulating factor) is a 26 kd cytokine that plays a major role in the acute phase response, especially the hepatic aspects of the acute phase response. Patients with alcoholic hepatitis manifest many aspects of the acute phase response. In this 6-month study we evaluated serial plasma interleukin-6 levels in 30 consecutive patients with moderate to severe alcoholic hepatitis. Mean admission plasma interleukin-6 activity was markedly increased (49.8 +/- 8.5 U/ml, normal less than 5 U/ml) in patients with alcoholic hepatitis, and levels decreased with clinical improvement to 15.6 +/- 6.1 U/ml at 6 months. Admission interleukin-6 activity correlated significantly (r = 0.82) with the severity of liver disease as assessed by the discriminant function of Maddrey. Also measured were selected assays postulated to be regulated by interleukin-6, including serum albumin (2.3 +/- 0.1 gm/dl), which was significantly depressed; alpha 1-acid glycoprotein (52 +/- 5 mg/dl), which was within normal limits; and IgA (827 +/- 70 mg/dl) and C-reactive protein (3.03 +/- 0.51 mg/dl), which were significantly elevated. Interleukin-6 activity fell over time in a pattern similar to that of bilirubin and C-reactive protein. We suggest that plasma interleukin-6 may not only regulate many aspects of the acute phase response but also may be a marker of inflammation and severity of disease in alcoholic hepatitis.