The expression of recombinant plasmids carrying the glpA gene (anaerobic glycerol-3-phosphate dehydrogenase) and the closely linked glpT gene (glycerol 3-phosphate transport) were studied under aerobic and anaerobic conditions. When the pattern of expression of enzymatic activity in different strains was compared with sodium dodecyl sulphate - polyacrylamide gel electrophoresis (SDS-PAGE) analysis from the same cells the glpA products were identified. Two polypeptides of 62 000 and 43 000 relative mass correlated with enzymatic activity. Five recombinant plasmids that contained one or both of the glpT of glpA genes were isolated and subjected to restriction endonuclease cleavage analysis. The regions of overlap from the inserts in these plasmids allowed definition of the regions of DNA containing the glpT and glpA genes. SDS-PAGE analysis revealed a partial product of the glpA locus from one plasmid, pLC42-17, which allowed more precise definition of the glpA locus on the physical DNA map and prediction of the direction of transcription.