AIMS: Pexelizumab, a monoclonal antibody inhibiting C5, reduced 90 day mortality and shock in the COMplement inhibition in Myocardial infarction treated with Angioplasty (COMMA) trial without apparent reductions in infarct size. Inflammation is a critical component of ST-elevation myocardial infarction (STEMI); this substudy examines prognostic values of selected markers and treatment effects. METHODS AND RESULTS: C-reactive protein, interleukin-6 (IL-6), and tumour necrosis factor-alpha (TNF-alpha) serum levels were assessed in 337 patients enrolled in either the placebo or the pexelizumab 24 h infusion group. Higher C-reactive protein and IL-6 levels at baseline, 24 h, and 72 h were strongly associated with increased subsequent death (P<0.002 at baseline and 24 h, P<0.02 at 72 h); and all baseline marker levels with death or cardiogenic shock (P<0.03) within 90 days. C-reactive protein and IL-6 levels were similar at baseline, but significantly lower 24 h later with pexelizumab, when compared with placebo (17.1 vs. 25.5 mg/L, P=0.03 and 51.0 vs. 63.8 pg/mL, P=0.04, respectively). At 72 h, corresponding levels were similar, whereas TNF-alpha was slightly higher (P=0.04) in the treated group. CONCLUSION: Inflammation markers and their serial changes predict death and shock in patients with STEMI undergoing primary angioplasty. Pexelizumab reduced C-reactive protein and IL-6, suggesting treatment benefits mediated through anti-inflammatory effects.