Alginate is produced as an exopolysaccharide by many fluorescent pseudomonads. However, pseudomonads often have a nonmucoid phenotype in standard laboratory media. Growth in the presence of 0.3 M sodium chloride or 3-5% ethanol reportedly can lead to the generation of mucoid variants of nonmucoid strains of Pseudomonas aeruginosa. We wished to determine whether alginate production by other fluorescent pseudomonads is affected by sodium chloride and ethanol. Eight alginate-producing strains of saprophytic and phytopathogenic pseudomonads were grown as broth cultures containing 0-0.7 M sodium chloride or 0-5% ethanol for 24-30 h at 28-degrees or 35-degrees-C. Culture supernatant fluids were subjected to ethanol precipitation, and the amount of alginate present was estimated by measuring the uronic acid content. The presence of sodium chloride and ethanol caused significant stimulation of alginate production by all strains tested except P. viridiflava ATCC13223 and P. fluorescens W4F1080. The optimal concentration of sodium chloride ranged from 0.2 to 0.5 M; that for ethanol ranged from 1 to 3%. Moreover, inclusion of the nonmetabolizable, nonionic solute sorbitol showed a similar stimulation of alginate production. The stimulation of alginate production by high medium osmolarity and dehydration appears to be a trait shared by fluorescent pseudomonads.