Intact and ovariectomized, non-arteriosclerotic female rats and arteriosclerotic, breeder female rats were subjected to myocardial infarction by the administration of 2 subcutaneous injections, 24 hr apart, of the beta-adrenergic stimulator, isoproterenol. The animals were sacrificed at regular hourly intervals following each injection and then on days 4, 6, 8, 10, 12, and 16 thereafter. Measurement of serum insulin and free fatty acids (FFA) demonstrated a blunted response in these metabolic parameters in the case of the ovariectomized virgin rats. The non-arteriosclerotic, intact virgin rats exhibited dynamic changes in serum insulin, glucose, FFA and corticosterone (Cmpd. B) following both isoproterenol injections, whereas the arteriosclerotic breeder rats manifested elevated levels of these parameters on Day 1, but did not display any increases in serum levels, except for FFA, following the second isoproterenol injection on Day 2. In spite of the hormonal alterations brought about by the gonadectomy and their differing metabolic response, the ovariectomized females did not have a mortality rate significantly different from the intact females. Thus, the presence or absence of ovarian estrogens seemingly does not affect the progress of an isoproterenol-induced myocardial infarction.