Approximately 20 different bacterial strains were isolated from aged (3 to ca. 70 years old) silk samples from Italy and kimono linings from Japan. Six different isolates were found capable of colonizing fibroin fabric in the laboratory, and four of them were found to utilize the protein as a sole source of carbon and nitrogen for growth. Among these isolates a Bacillus subtilis and a Micrococcus luteus were selected for further studies, as they appeared to be endowed with a pronounced hydrolytic activity of purified silk fibroin. Both species produce more than one protease active on casein and fibroin and the proteolytic activity of M. luteus isolate is totally dependent on the presence of Ca++ ions. Work is underway to separate and characterize the different proteases produced by the two bacteria and to ascertain if fibroin is degraded by a specific hydrolase or rather by enzymes whose main substrates are other proteins.