Feasibility and engineering aspects of biological sulphate reduction in gas-lift reactors were studied. Hydrogen and carbon dioxide were used as energy and carbon source. Attention was paid to biofilm formation, sulphide toxicity, sulphate conversion rate optimization, and gas-liquid mass transfer limitations. Sulphate-reducing bacteria formed stable biofilms on pumice particles. Biofilm formation was not observed when basalt particles were used. However, use of basalt particles led to the formation of granules of sulphate-reducing biomass. The sulphate-reducing bacteria, grown on pumice, easily adapted to free H2S concentrations up to 450 mg/L. Biofilm growth rate then equilibrated biomass loss rate. These high free H2S concentrations caused reversible inhibition rather than acute toxicity. When free H2S concentrations were kept below 450 mg/L, a maximum sulphate conversion rate of 30 g SO42-/L.d could be achieved after only 10 days of operation. Gas-to-liquid hydrogen mass transfer capacity of the reactor determined the maximum sulphate conversion rate.