Two seed characteristics of grain and forage sorghum were studied to determine the extent to which they were associated with viability and vigor. These characteristics were seed size and specific gravity. Fifty seed were obtained from the Mississippi State Seed Testing Laboratory. Twenty-five lots were separated into three size classes designated as large, medium, and small. The other twenty-five lots were separated into three specific gravity cclasses and designated as light, medium, and heavy. The physiological quality of seed from various seed sizes and specific gravity classes of each lot was evaluated for vaibility by the standar germination test and for vigor by the accelerate aging technique and filed emergence response. There was no consistent relationhip between seed size and viability of processed lots of seed. Each seed lot reacted differently, and there was considerable variations among the lots. Specific gravity seemed to be more consistently related to viability in processed lots than was seed size. In general, in each seed lot, an increase in specific gravity of the seed was accompanied by an increase in germination. Accelerated aging technique as a test for seed (capacity to germinate and emerge after being stressed) revelated that seed of the small size and those of light weight were more inferior after accelerated aging than the other size ans weight classes. In general, large, heavy seed gave better responses than did small, light seed. In the field emergence experiment, the relationships (...).