An appropriate tester correctly identifies the relative performance of experimental lines while maximizing the differences between lines. Most sorghum breeding programs use elite inbred lines testers. Inbred line testers evaluate experimental lines against a specific genetic background, possibly increasing the probability of incorrectly discarding material. A potential solution would be to use F1 testers that combine two genetic backgrounds. The purpose of this research was to compare F1 testers versus inbred line testers for evaluating experimental sorghum lines in testcrosses Line x tester analyses were performed to assess tester consistency in assigning ranks. With one exception, all of the line x tester analyses were non-significant, indicating that the testers provided similar evaluations of the experimental lines. Correlations between the ranking of the experimental lines by their average performance and the rank assignments of each tester were measured to further asses tester accuracy. In all cases, the rank correlations were highly significant, implying that all of the testers accurately ranked experimental lines. In addition, all of the testers consistently identified the majority of the top performing experimental lines despite some important rank shifts. F-ratios for variance among the experimental lines (entry effect) were compared with the Schumann-Bradley statistical test to compare efficiencies. With one exception, the F1 testers always produced the largest or second largest entry effect F-ratio. Where the F1 testers produced the second largest F-ratio, it was not declared statistically different from the largest F-ratio by the Schumann-Bradley test, indicating that the testers had similar discriminatory efficiencies. Testcross variances were measured to further compare discriminatory efficiencies. With one exception, the F1 testers consistently produced the largest variances, evidence that the F1 testers were effective in maximizing differences among the experimental lines. The results indicate that F1 testers represent valid testers for evaluating experimental sorghum lines against two genetic backgrounds in a single testcross.