Protein-energy malnutrition is common in patients with inflammatory bowel disease requiring surgery. Increased morbidity from sepsis may be associated with pre-operative weight loss due to associated diminished cellular immune defence mechanisms. Eighteen patients with Crohn's disease requiring elective abdominal surgery were divided into three nutritional groups before and after surgery, defined by their weight loss. The groups were well matched for other clinical variables. Delayed hypersensitivity skin reactivity to multiple antigens was measured before operation and during convalescence. The delayed hypersensitivity skin reactivity was depressed in the malnourished patients both pre-and post-operatively, although clinical outcome from surgery was not affected by nutritional status.