The effects of pesticide endosulfan (an organochlorine compound), on the ovaries of bluegill fish (Lepomis macrochirus) were studied. Exposures for 24 hs with histological preparations at 25% (0.25 Î¼g/L), 75 % (0.75 Î¼g/L), and 100 % (1 Î¼g/L) sub lethal concentrations were examined. The control contained an abundance of the different stages of oocytes (Oocytes I, II, III, and IV) and had an intact ovigerous lamellae and follicular lining. The control also contained a thick and complete ovarian wall with evident provitelline and euvitelline nucleoli. After 24 hr exposure to a 25% concentration, many Oocyte II and III cells had damaged stroma and cytoplasmic and nuclear retraction. Adhesion is pronounced at the 25% concentration, but is even more profound at the 75% concentration. Empty follicles and a unique cytoplasmic clumping can be observed in Oocyte III and IV cells in the 75% concentration. The ovaries of fish exposed to a 100% concentration display an immense amount of empty follicles along with necrosis of nuclei and expelled nuclei. As the concentration increased, the amount of atretic cells increased, and the ovarian wall became more thinned and lifted. Macrophages were more evident as the concentration increased and the sizes of the different stages of oocytes ,exposed to the different concentrations became smaller as well. This study showed that there is a clear correlation between the amount of damage seen and the amount of endosulfan.