Hybrid grain sorghum seeds were aged artifically for 0, 3, 5, 7, and 11 days at 42oC and 100% RH, wich produced high, medium, low and lowest vigor level. Among the various laboratory tests performed, standard germination and field mergence, were the least sensitive in discerning the physiological condition of the seed lots. The speed of germination more accurately differentiated the degree of deterioration of the seed lots and was closety correlated to yield. Adverse effect of planting low vigor seeds was found to be related to plant height, panicle exsertion, anthesis, tillering capacity, length of the panicle, and yield. Less vigours seeds produced plants which were not able to "catch up" to the vigorous ones. These slow growing plants were significantly inferior in panicle exsertion to those produced from more vigorous seeds. Seeds aged for 7 and 11 days had their process of exsertion delayed for about 2 and 3 days, respectively. Anthesis, conseguently, was also significantly retarded. Tillering capacity of plants produced from low vigor seeds was significantly reduced, as well as grain yield. Primary head yield was also significantly reduced about 14% for the more deteriorated seeds, and 12% for the mixed treatment, as compared to the control. Yield reductions of 9, 4, and 3% were also detected in seeds aged for 7, 5, and 3 days, respectively, as compared to the check. Seed moisture content generally increases as the vigor level decreased, indicating that the process of maturation was delayed as a (...).