The invention relates to a process for the removal of, H.sub.2S and mercaptans from a gas stream comprising these compounds, which process comprises the steps of: (a) removing H.sub.2S from the gas stream by contacting the gas stream in a H2S-removal zone with a first aqueous alkaline washing liquid to obtain a H.sub.2S-depleted gas stream and a sulphide-comprising aqueous stream; (b) removing mercaptans from the H.sub.2S-depleted gas stream obtained in step (a) by contacting the H.sub.2S-depleted gas stream in a mercaptan-removal zone with a second aqueous alkaline washing liquid to obtain a mercaptan-depleted gas stream and an thiolate--comprising aqueous stream; (c) contacting the combined aqueous streams comprising sulphide and thiolates obtained in step (a) and step (b) with sulphide-oxidizing bacteria in the presence of oxygen in an oxidation reactor to obtain a sulphur slurry and a regenerated aqueous alkaline washing liquid; (d) separating at least part of the sulphur slurry obtained in step (c) from the regenerated aqueous alkaline washing liquid; and (e) recycling the regenerated aqueous alkaline washing liquid to the H.sub.2S-removal zone in step (a) and to the mercaptan-removal zone in step (b). The invention further relates to a gas-treating unit for the removal of H.sub.2S and mercaptans and from a gas stream comprising these compounds in a process according to the invention.