The air samples collected at various stages of concd. H2SO4 and TiO2 prodn. were studied for the acid content. The highest concs. of the acid in the thoracic fraction were found at the point of sampling a mixt. contg. 30% H2SO4, at the emitter as well as at the clarifier. They were 10.32, 10.92 and 35.5 mu g/m(3), resp. The concns. of the inhalable fraction taken at the same points were 28.42, 16.55 and 85.8 mu g/m(3), resp. Thoracic fractions of H2SO4 constituted 26-95% of inhalable fraction, depending on the type of sampling and analyzed process.