The study examined brown cells of oysters, Crassostrea virginica, as potential indicators of pollution related stress. Regardless of collection station brown cells increased in connective tissue when it was inflamed. Significantly fewer brown cells were observed in connective tissue of oysters from the clean versus the contaminated station; no significant differences in size were apparent in brown cells or vesicles between the two stations. Brown cell vesicles in connective tissue of oysters from the clean station were a translucent light-brown color with inclusions in the larger vesicles, whereas in oysters from the contaminated station they were blackish-brown with 2-3 inclusions in all vesicles regardless of size. Auricles in oysters at the clean station had significantly more brown cells which were larger and contained more vesicles than those at the contaminated station. Studies indicate that vesicles of oyster brown cells are lysosomes and these cells possess the requisites for detoxification and have the potential for use as a biomarker of exposure to contaminants and stress.