In evaluating exotic germplasm for its potential to improve a crop species, it is important to know which accessions possess the greatest relative numbers of favorable alleles for a trait or traits of interest. Dudley's test of favorable alleles offers plant breeders the ability to evaluate a set of potential donors of favorable alleles with reference to a particular elite hybrid, and to rank the lines according to their respective ability to improve that particular hybrid. A set of 29 genetically diverse sorghum accessions were crossed with sterile versions of three U.S.- adapted grain sorghum lines (BTx623, BTx631, and RTx430). The hybrids were sown in a growth chamber programmed to simulate diurnal temperature cycles in Lubbock, Texas for the dates March 15 – April 15, inclusive. Experimental design was a complete lattice with nine replications. Data collected included rate of emergence (expressed as emergence index), total emergence, and seedling fresh weight. Dudley's test of favorable alleles was conducted, using both ATx623*RTx430 and ATx631*RTx430 as the reference hybrids. The magnitude and direction of the relative contribution of a particular line often varied according to the elite hybrid under consideration for improvement. Despite these differences, results indicate that a number of lines from quite divergent taxonomic classes and geographic origins possess the ability to improve the early season cold tolerance of grain sorghum within the U.S.