Heat-tolerant and -sensitive Lycopersicon esculentum Mill. and L. pimpinellifolium (Jusl.) Mill. genotypes were grown in the greenhouse under optimum- (27/23C, day/night) and high-temperature (35/23C) stress regimes. Heat tolerance levels in the genotypes were established by determining percent fruit set at high and optimum temperatures. Under optimum temperature, fruit set ranged from 41% to 84% and from 45% to 91% in the heat-sensitive and heat-tolerant genotypes, respectively. Under high temperature, no fruit set in the most heat-sensitive genotypes. Fruit set in the heat-tolerant genotypes ranged from 45% to 65%. In vitro germination and tube growth of pollen taken from genotypes grown under optimum temperature conditions were determined before and after subjecting the pollen to 45C for 1, 2, and 4 hours. The response of pollen to heat treatments was genotype dependent and not a general predictor of fruit set under high-temperature stress.