Scanning electron microscopy was utilized in evaluating inner surfaces of rubber and silastic® teat cup inflations. New inflations and inflations subjected to 1000 and 5000 or more milkings were examined. Cracks and depressions appeared in new rubber inflations and increased in width (from 1.0 μm to 15.0 μm) with use. No cracks were visible in the silastic® product. Bacteria appeared to be present in the cracks of the inner surface of used rubber inflations but were not present in silastic ®.