Utilising an "agar well diffusion assay", we determined production of an inhibitory compound (bacteriocin) from Serratia marcescens Bn10 strain isolated from hazelnut beetle, Balaninus nucum L. (Coleoptera: Curculionidae). It was active against Bacillus subtilis, Corynebacterium xerosis, Enterobacter cloacea, Escherichia coli, Proteus vulgaris, Klepsiella pneumonia, Neisseria flavescens, Pseudomonas aeruginosa, Salmonella typhimurium and Serratia marcescens, but not active against Citrobacter freundii, Staphylococcus aureus and Streptococcus faecalis. Partial characterisation indicated that bacteriocin was heat stable, for activity remained after heating at 121 degreesC for 15 min. It was inactivated by trypsin, proteinase K and protease; however, it was not inactivated by lysozyme. The agent was also stable at pH values from 2,0 to 10,0. Since S. marcescens Bn10 did not contain plasmid, the gene encoding for the bacteriocin is presumably located on the chromosome.