Physiological characteristics of DBT desulfurization and cell growth of Gordonia sp. CYKS1 were investigated. It exhibited a preference to ethanol in a medium containing two carbon sources, ethanol and one of the carbohydrates used, glucose, sucrose, maltose, and galactose although it consumed both carbon sources simultaneously. Cell growth on ethanol or glucose followed the Monod kinetics. The optimal range of pH for the desulfurization of DBT and the cell growth was 7 to 8. The desulfurization rate decreased about 30% at pH 6, and no significant desulfurization or cell growth was observed at pH 5. As the initial DBT concentration increased up to 1.5 mM, the desulfurization rate also increased while no significant changes in the growth rate were observed. The maximum desulfurization rate was 12.50 mumol L-1 h(-1) at an initial DBT concentration of 1.5 mM. Cell growth and desulfurization activity were severely inhibited by the presence of 2-hydroxybiphenyl (2-HBP). When 0.05 mM of 2-HBP was added at the beginning, both of the desulfurization rate and cell growth rate decreased about 20%. It was found that cell growth and desulfurization were completely inhibited in the presence of 2-HBP at 0.15 mM or a higher concentration. The inhibition by 2,2'-dihydroxybiphenyl (DHBP) was less severe than 2-HBP. About 80% of desulfurization activity was retained in the presence of 2,2'-DHBP at 0.4 mM.