The anaerobic oxidation of dissolved hydrogen sulfide to sulfate was studied at 30degreesC and pH 7.0+/- 0.3 in a continuous culture of the chemoautotrophic bacterium Thiobacillus denitrificans. During the microbial oxidation, the concentration of dissolved hydrogen sulfide as the energy source and electron donor decreased simultaneously with the concentration of nitrate as electron acceptor. The number of free cells formed in the culture was proportional to the amount of hydrogen sulfide oxidized. and the growth yield was independent of the substrate concentrations. The specific growth rate was significantly dependent on the dissolved hydrogen sulfide concentration (0.03-3.61 mol.m(-3)) and nitrate concentration (0.02-19.5 mol.m(-3)). The kinetic data were analyzed with a rate expression as a function of each rate-limiting factor. The anaerobic chemoautotroph T. denitrificans was capable of oxidizing dissolved hydrogen sulfide at a maximum of 0.566X10-(14)mol.h(-1).cell(-1).