During the course of our screening program for new antimicrobial agents two chemically-related substances, pyracrimycins A and B, were isolated from a Streptomyces strain. The producing organism, isolated from a soil sample collected in Pavia (Italy) was named Streptomyces eridani Coronelli et al. n. sp. (ATCC21619). The present paper deals with the description of the producing strain, the isolation of the two metabolites and the biological properties of the two metabolites. Pyracrimycin B is biologically inactive whereas pyracrimycin A is active in vitro against both Gram-positive and Gram-negative bacteria.