The genes coding for the protease inhibitors, SSI and API-2c', have been analyzed by comparing DNA macrorestriction patterns of Streptomyces albogriseolus S-3253 and S. griseoincarnatus KTo-250 with those of inhibitor-deficient mutants. The mutants were found to suffer from chromosomal deletions rather than plasmid loss which resulted in the loss of the relevant genes. Hybridization experiments indicated that the ssi homologs in S. lividans and S. coelicolor A3(2) are located near the end of the linear chromosome.