A mathematical model is proposed for the growth of Thiobacillus ferrooxidans in the process of Fe2+ oxidation depending on the active acidity and temperature of the medium. The model was used to establish the correlation between the action of temperature and pH of the medium on the bacterial growth and oxidation of Fe2+. The range of pH values which had no effect on the bacterium is broader at 28 degrees C (from 2.5 to 2.8) than at 12 degrees C (from 2.3 to 2.4). Apparently, the growth of the bacterium and the enzymatic processes of Fe2+ oxidation are more susceptible to changes in the pH than in temperature, at least when it is lowered to 12 degrees C.