Myocardial necrosis was induced in 200 male rats by administration of isoproterenol. Seventy-two of the 139 survivors were treated with dimethylsulfoxide and 67 received no further drugs. Animals from each group were killed 2, 7, and 14 days after induction of necrosis, along with 10 control rats. Hexosamine and hydroxyproline determinations were made on the hearts, and the values obtained were compared between groups. A transient rise in cardiac hexosamine of similar degree was found in both the dimethylsulfoxide-treated and untreated groups as compared to the controls. A marked elevation in cardiac hydroxyproline levels was noted at all three times in both groups with cardiac necrosis. The levels in the dimethylsulfoxide-treated groups were, however, significantly lower than those of the untreated group. These studies indicate that, although the early myocardial lesions in the treated and untreated groups were of equal severity, dimethylsulfoxide modified the healing process so as to result in a reduced area of myocardial scarring.