Major surgery suppresses host immune reactivity through alterations in monocyte and T cell‐derived cytokine, eicosanoid and acute‐phase protein release. Recombinant interleukin (IL) 2 augments T lymphocyte and monocyte activity in vitro. Eighteen patients, with localized colorectal cancer, were randomized to receive either recombinant IL‐2 or placebo for 3 days by subcutaneous injection before surgery. Serum levels of IL‐1β, IL‐6, tumour necrosis factor α, soluble IL‐2 receptor, C‐reactive protein (CRP) and albumin were measured, and T lymphocyte surface expression of HLA‐DR and CD25 and neutrophil phagocytosis were determined, before and for 21 days after surgery. Significant augmentation of IL‐6, CRP and soluble IL‐2 receptor production, enhanced expression of activation markers and increased neutrophil activity were found. Recombinant IL‐2 may have a role in ameliorating immunosuppression found after major surgery.