Three different strains ofThiobacillus ferooxidanswere grown in aqueous ferrous sulfate solutions at 30.5°C and at pH 2.0 in a bioreactor. Their specific growth rate followed Monod kinetics. Their maximum specific growth rate (μm)was between 0.138 and 0.148 h−1and their saturation constant (Ks) was in the range from 0.338 to 0.479 g Fe2+/L. Comparing our data with other data from the literature, we concluded that the kinetics of ferrous iron oxidation is independent of the strain used. A good approximation of the growth kinetics on ferrous iron ofThiobacillus ferrooxidansbetween 20 and 32°C and pH 2.0–2.5 is obtained by using μm= 0.14 h−1Ks= 0.4 g Fe2+/L