To study the association of increased serum group II phospholipase A2 concentrations to C-reactive protein concentrations in the sera of critically ill surgical patients. Prospective study. Surgical intensive care unit (ICU) of a university hospital. Sixty-seven consecutive patients admitted to the surgical ICU. The catalytic activity of phospholipase A2 and the serum concentrations of group II phospholipase A2 and C-reactive protein were measured daily during each patient's stay in the ICU. A total of 205 blood samples were taken. In addition, the preoperative serum levels of group II phospholipase A2 were determined in patients admitted for cardiac surgery. Serum group II phospholipase A2 values correlated statistically significantly with the catalytic activity of phospholipase A2 and serum C-reactive protein values. In particular, severe infections, diseases involving tissue destruction, and elective operations per se, caused considerable increases in serum group II phospholipase A2 concentrations. Our results support the earlier presented idea that group II phospholipase A2 is an acute-phase reactant. (Crit Care Med 1994; 22:956–959)