High temperature in general was found to be the major factor affecting symbiotic nitrogen fixation. High temperature of 35EC when applied to the roots only didn’t effect nitrogen fixation. However, small variances were recorded at 40EC in all cultivars. Fixation was severely inhibited at 45EC in all cultivars. The cultivar sable was found to be the most tolerant to high temperatures and it also recovered from heat stress better than the other cultivars. Although, cultivar bragg was not as heat tolerant as other but this recover better then other cultivars studied. Which were very similar in their sensitivities to heat stress.