The morbillivirus epizootic during 1990 to 1992 in Mediterranean striped dolphins (Stenella coeruleoalba) off the Mediterranean coast of Spain diminished these populations directly through mortalities, and indirectly through loss of normal fecundity. High levels of polychlorinated biphenyls (PCB's) also were detected in stranded animals. In addition to high numbers of abortions during the epidemic, unusual cystic structures were noted in the ovaries of several morbillivirus-infected dolphins with high PCB levels. These structures were identified as multiple luteinized cysts from their gross and histomorphologic characteristics. No morbillivirus antigens were detected in the lesions by immunohistochemistry. Because luteinized cysts occur when ovulation is impeded, either an effect of morbillivirus or PCB's on hypothalamic/pituitary function or an effect of PCB's on ovarian responsiveness are proposed as pathogenic mechanisms. These cysts may impede population recovery from the epidemic if similar cysts occurred on surviving dolphins.