Previous Studies have shown that seed density and moisture deficits affect germination and early seedling growth of cotton (Gossypium hirsutum L.). High-density seeds contain a higher lipid:protein ratio than do low-density seeds, reflecting the contribution of the hydrophobic lipid fraction to the degree of seed fill. Possible associations among seed density, water potential and imbibitional hydration were investigated in a model system using aerated solutions in a 30 C water bath. Increasing seed density from 1.00 to 1.12 g/ml produced a nearly-linear 37% reduction in water uptake in the first 4 h of imbibition, differences that were sustained at least through the next 4 h. Adjusted for seed weight, variation in water uptake created a 20% differential in relative water content at 4 h. Lowering the water potential to -5 bars with PEG 8000 reduced water uptake by about 16% for all seed densities. Parallel germination studies in growth chambers produced contrasting effects of increasing; seed density and decreasing water potential: final germination of high-density seeds was significantly higher than that of low density seeds, but that of all seeds was lowered by PEG-reduced water potential. Restricted water uptake may be a physiological response to the combined effects of density classification and seed composition, but it also appears to be a physical response to the barrier to imbibition produced by reductions in water potential with PEG. Even though the physiological and physical factors each influenced the rate of water uptake by cotton seeds, there was no significant interaction between the two. Consequently, the rate of water uptake per se does not determine the final level of germination, though it may influence its rate.