Choice of the appropriate tester for the evaluation of corn inbred lines is of major concern among corn breeders. Hence, comparisons among different testers are needed to determine their effectiveness in selecting inbred lines and in population improvement programs. Also, it is to determine whether to test the lines of corn early or late during the inbreeding process. Knowledge of the relationships between the mean yield of the lines per se and their testcrosses also is important. My objectives were to: 1) determine if there were significant differnces among S1 testcrosses, among S8 testcrosses, and between S1 versus S8 testcrosses, 2) compare the genetic variation among the different sets of testcrosses, 3) determine the relationships of inbred line performance among the different types of testers, and 4) compare the relation of testcross performance to line per se performance. Highly significant differences among the S1 and among the S8 testcorsses were found for all the traits. No significant differences, however, were detected between the S1 versus the S8 testcrosses for most of the traits. Genetic variance among the different S1 line and S8 line testcrosses was as theoretically expected for the related testers. That is, greater testcross genetic variance with the low yielding tester than the high yielding tester at both the S1 and S8 levels. S1 line testcrosses made with an unrelated high yielding tester, however, had the greatest genetic variance. Use of an unrelated high yielding inbred line was, (...).