OBJECTIVE: The No-React process for biomaterials was suggested to prevent calcification and degeneration. We examined in vivo in a chronic sheep model the performance of a Biocor bovine internal mammary artery (BIMA) graft after No-React processing. METHODS: 'No-React' processing consists of aldehyde cross-linkage following a detoxification process with multiple physical variables and incubation with surfactant. Biocor BIMA No-React treated grafts have been interposed in the carotid artery in seven sheep with a Dacron graft as control. Grafts were explanted after 3 or 6months and were grossly examined, by X-ray, histology, transmission and scanning electron microscopy, and atomic absorption spectrophotometry. RESULTS: In the BIMA, good healing was found with a smooth intimal surface, minimal inflammatory reaction, and a well preserved ultrastructure. Calcification increased progressively. In the Dacron grafts, a fibrous covering the inner surface and infiltration with fibroblasts, histiocytes and macrophages was noted. Calcium content was stable. CONCLUSION: Calcification increased progressively in Biocor BIMA No-React grafts. Minimal inflammatory changes, a smooth inner surface and well preserved ultrastructure were noted.