Bioremoval of H2S from gas streams became popular in recent years because of high process efficiency and low operational costs. To expand the scope of these processes to gas streams containing volatile organic sulfur compounds, like thiols, it is necessary to provide new insights into their impact on overall biodesulfurization process. Published data on the effect of thiols on biodesulfurization processes are scarce. In this study, we investigated the effect of methanethiol on the selectivity for sulfur production in a bioreactor integrated with a gas absorber. This is the first time that the inhibition of biological sulfur formation by methanethiol is investigated. In our reactor system, inhibition of sulfur production started to occur at a methanethiol loading rate of 0.3 mmol L(-1) d(-1). The experimental results were also described by a mathematical model that includes recent findings on the mode of biomass inhibition by methanethiol. We also found that the negative effect of methanethiol can be mitigated by lowering the salinity of the bioreactor medium. Furthermore, we developed a novel approach to measure the biological activity by sulfide measurements using UV-spectrophotometry. On the basis of this measurement method, it is possible to accurately estimate the unknown kinetic parameters in the mathematical model.