Abstract: A biological conversion process is provided for degradation of sulfur-containing pollutants such as H.sub.2 S, CS.sub.2, COS, and also organic surfur compounds such as thio-alcohols, thio-ethers, and thiophenes in waste gas. A packed reactor is provided which has packing material covered with immobilized microorganisms of the family of Thiobacillaceae and which are continuously kept moist, so that metabolic products of the microorganisms are dissolved in the moisture and discharged continuously. A continuous concentration gradient for sulfate ions thereby results in the reactor or in the region of the microorganisms, these sulfate ions being neutralized in a second reactor by supplying lye (soda or potash lye) forming readily-soluble salts.