To evaluate true ileal digestibility of bovine immunoglobulins, seven healthy human adults ingested a 15N-labeled preparation of an immunoglobulin concentrate. After fasting overnight, subjects drank 400 mL of immunoglobulin concentrate (77 mmol), and ileal effluents were collected for 8 h at 20-min intervals using a naso-intestinal intubation technique. In addition to osmolality and pH, the concentrations of exogenous and endogenous nitrogen and ions (Na+, K+, Cl-, Ca2+, Mg2+) in the effluents were measured. Bovine immunoglobulin concentrations (IgG, IgM, IgA) were estimated by a radial immunodiffusion technique. The mean flow rate of the liquid phase was 22.3 +/- 6.1 mL/20 min and did not vary significantly during the collection period. No change was observed for osmolality, pH or Na+, K+ and Cl- concentrations. Two hours after meal ingestion, Ca2+ and Mg2+ concentrations increased significantly (P < 0.05). The recoveries of nitrogen of ingested IgG and IgM still immunologically active were 19 +/- 3% and 19 +/- 4%, respectively. No IgA was detected in the ileum. Mean digestibility of the exogenous nitrogen fraction was 79 +/- 3%. In comparison to literature data, which show that other milk proteins have ileal digestibilities of > 90%, our results demonstrate a lower ileal digestibility of bovine immunoglobulins in humans.