The growth kinetics of Thermus thermophilus HB27 was investigated in rich medium (Thermus medium) under batch cultivation at 65 degreesC in 3-l fermentors. The growth and oxygen consumption rates were highly dependent on the aeration and agitation rates. Volumetric mass transfer coefficient (K(L)a, h(-1)) and hence oxygen transfer rate (OTR, mol m(-3) h(-1)) into the fermentation broth increased with increased aeration and/or agitation rates. A K(L)a and OTR of 175.4 h(-1) and 31.7 mol m(-3) h(-1) respectively, corresponding to 500 rpm agitation and 2 vvm aeration with a mixture of air and oxygen, were required to avoid oxygen limitation. The maximum growth rate (mu(max), h(-1)), doubling time (t(D), h), and dry cell weight determined for T. thermophilus HB27 growing under, these conditions were 0.27 h(-1), 2.67 h, and 3 g/l respectively. This cell yield is higher than any previously published reports for growth of Thermus cultures, including studies that employed pressurized bioreactors.