Thermotolerant strains of Rhizobium leguminosarum biovarphaseoli were isolated from nodules of Phaseolus vulgaris grown in Kenyan soils, where high soil temperatures often exceed 40°C during sunny days. The isolates varied in their maximum growth laboratory temperature with two strains, 17 and 29B, able to grow at 42°C on yeast extract/mannitol agar media and at 40°C in liquid medium. These strains also survived better in moist clay soil at 38°C and 42°C and on seeds at room temperature but did not grow as well as several of the other strains at low pH. The thermo-tolerant strains nodulated three bean cultivars in a rooting medium that attained a daily maximum temperature of 36°C to 40°C but they varied in effectiveness according to the cultivar used.