Sorghum (Sorghum bicolor (L.) Moench) is a major summer cereal, primarily grown asa dryland crop in semiarid, subtropical and tropical environments. High temperature conditions are often experienced around flowering, and this exposure is likely to increase due to projected climate change. High temperature around flowering has deleterious effects on seed set and could be a major factor limiting yield. The objectives of this study were to (1) examine the responses of seed set to a range of high temperature conditions,(2) explore the extent of genotypic variation among temperature responses of sorghum genotypes in controlled environment facilities (CEF), and (3) determine whether the effects of heat stress observed in CEF are representative of those in the field. Eighteen diverse sorghum genotypes were grown at day/night temperatures of 30/21ºC, 33/21oC, 36/31oC, and 38/21ºC in CEF experiments. Genotypes differed in their responsiveness to temperature with respect to threshold temperature for effect on seed set and nature of the response. Seed set was strongly correlated with pollen viability across all experiments. Six contrasting genotypes selected from the CEF experiment were grown in a solarweave-covered tunnel in the field, which provided a 6-8oC increase in temperature in comparison to ambient conditions. The experiment contained two treatments and two sowing dates to provide four temperature regimes. The result from the field experiment reflected those found in the CEF experiments and confirmed the finding that yield loss of sorghum under increased temperature was a consequence of reduced seed set. The observed genetic variation in pollen and seed-set traits could be exploited through breeding to develop heat tolerant varieties for future climates.