A chitinase gene from the Gram-negative bacterium Serratia marcescens BJL200 was cloned in Lactococcus lactis subsp. lactis MG1363 and in the silage inoculum strain Lactobacillus plantarum E19b. The chitinase gene was expressed as an active enzyme at a low level in Lactococcus lactis, when cloned in the same transcriptional orientation as the gene specifying the replication protein of the vector pIL253. Using the expression vectors pMG36e and pGKV259 with lactococcal promoter fragments p32 and p59, the expression in L. lactis was increased nine- and 27-fold, respectively. An additional twofold increase was obtained after cloning the gene under the control of p59 in the high-copy number replicon pIL253. In Lactobacillus plantarum, chitinase activity was expressed from p32, and the activity was at the same level as under p32 control in L. lactis.