Glucose-6-phosphate dehydrogenase (G6PD) is present in different mixtures of interchangeable states of aggregation in each of the supernatant and pellet fractions of unfertilized and fertilized sea urchin eggs. These states are each altered differently by redox agents, as shown by changed electrophoretic isozyme patterns and altered filtration retention following treatment by diamide, oxidized glutathione, reduced glutathione, ascorbate, or dithiothreitol. Activity levels of G6PD are altered by redox agents, probably as a result of change in aggregation state or change in association with inhibitory associated molecules. This suggests that there are control mechanisms for G6PD that are in different conditions in unfertilized vs. fertilized stages and supernatant vs. pellet compartments, resulting in different states of G6PD in the isolates.