A moderately halophiIic and halotolerant eubacterium, strain KS3, was isolated from a salty soil in Thailand and identified as Halomonas elongata based on the results of conventional taxonomic and DNA-DNA reassociation studies. H. elongata KS3 grows in the presence of 0.3 to 21% NaCl and at temperatures of 5 to 45 degrees C. The optimum concentration of NaCl and temperature far growth were 3 to 5% and 37 degrees C, respectively. Under hyperosmotic stress in a glucose-mineral medium, the accumulation of several low-molecular weight nitrogenous organic compounds was observed. These compounds were identified as 1,4,5,6-tetrahydro-2-methyl-4-pyrimidinecarboxylic acid (ectoine), 1,4,5,6-tetrahydro-2-methyl-5-hydroxy-4-pyrimidinecarboxylic acid (hydroxyectoine), gamma-N-acetyl-alpha,gamma-diaminobutyric acid (ADABA), and L-alanine. Ectoine production was induced immediately by the addition of NaCl and the amount accumulated increased with an increasing external concentration of NaCl and reached approximately 120 mu g.mg(-1) of dry cells at a concentration of 2.56 M NaCl. Hydroxyectoine was detected with a lag in time after the : addition of NaCl at a concentration greater than 1.71 M, and the amount accumulated increased and reached 45 mu g.mg(-1) of dry cells at a concentration of 2.56 M NaCI. Thus, hyperosmotic stress induced by salt appears to cause the accumulation of ectoine and hydroxyectoine as compatible solutes in H.. elongata KS3.