Biological adhesives are made of human plasma and bovine heterologous proteins. These entail a poorly documented risk of sensitization. We report about two allergic accidents caused by the injection of Tissucol in the pituitary mucosa of patients suffering from the Rendu-Osler-Weber disease. The clinical picture of the first case was that of a serum sickness, and leukocytoclastic vasculitis was demonstrated. The second case was a delayed hypersensitivity accident, which was confirmed by the subsequent allergological investigation. Although the responsibility of thrombin seems to be evidenced in these two cases, it nevertheless remains exceptional. However, the risk of sensitization following repeated injections of heterologous proteins in a mucosa with a particularly high immunological responsiveness must be well-known. The increasing use of these biological products will probably result in a growing number of accidents, and we must now contemplate the possibility of screening this sensitization before using biological adhesive. Finally, the possibility of latent sensitization by the ingestion of beef must also be considered.