Abstract. The aerobic biodegradation of high-concentration, to 24gl1, 2-propanol (IPA) by a thermophilic isolate ST3, identified as Bacillus pallidus, was successfully carried out for the first time. This solvent-tolerant B. pallidus utilized IPA as the sole carbon source within a minimal salts medium. Cultivation was carried out in 100-ml shake flasks at 60C and compared with cultivation within a 1-l stirred tank reactor (STR). Specific growth rate () was about 0.2h1 for both systems, with a maximum cell density of 2.4108cellsml1 obtained with STR cultivation. During exponential growth and stationary phase, IPA biodegradation rates were found to be 0.14 and 0.02gl1h1, respectively, in shake-flask experiments, whereas corresponding values of 0.09 and 0.018gl1h1 were achievable in the STR. Generation of acetone, the major intermediate in aerobic IPA biodegradation, was also monitored as an indicator of microbial IPA utilization. Acetone levels reached a maximum of 2.22.3gl1 after 72 and 58h for 100-ml and 1-l systems, respectively. Both IPA and acetone were completely removed from the medium following 160 and 175h, respectively, during STR growth, although this was not demonstrated within shake-flask reactions. Growth of B. pallidus on acetone or IPA alone demonstrated that the maximum growth rate () obtainable was 0.247h1 at 4gl1 acetone and 0.202h1 at 8gl1 IPA within shake-flask cultivation. These results indicate the potential of the solvent-tolerant thermophile B. pallidus ST3 in the bioremediation of hot solvent-containing industrial waste streams.