Heat stress is a powerful deterrent to successful flower fertilization and high seed yield.  This study was conducted to characterize the genetic variability in heat tolerance of pollen germination among soybean lines.  Maturity group four lines were planted in dryland and irrigated environments in a randomized complete block design with three replications.  Pollen was collected from field-grown plants throughout the flowering period from each plot in the early morning and subjected to incubation temperatures of 28, 34, and 38 ^oC in the lab.  Pollen germination rates decreased rapidly as incubation temperature increased.  Pollen germination rates were highest at 28 ^oC.  Genotypes differed significantly in pollen germination rates.  Genotypic response of pollen germination to environments and incubation temperature will be presented.