Lactococcus lactis produces polysaccharide under defined environmental conditions. Three approaches are being used to identify regulators of polysaccharide synthesis in the organism. i) Two new lactococcal vectors, each of which contains a promoterless reporter gene, have been developed. They are being used to select for chromosomal insertions that affect expression of polysaccharide ii) Genetic complementation with lactococcal genomic libraries identified two classes of lactococcal genomic activities, both of which affect capsule expression in Escherichia coli iii) Lon, a highly conserved protease, is a negative regulator of polysaccharide synthesis in E. coli. Antiserum specific to Lon protease reacted with a lactococcal protein similar in size to E. coli Lon. This reaction was strongest in lactococcal strains which could not be induced to express polysaccharide.