Increased oxidative stress and antioxidant deficit have been suggested to play a major role in adriamycin-induced cardiomyopathy and congestive heart failure due to multiple treatments with adriamycin (doxorubicin). In this study, we investigated the acute effects of a single dose of adriamycin on myocardial antioxidant enzymes in rats. Adriamycin (2.5 mg/kg) was injected (i.p.) and myocardial antioxidant enzyme activities, mRNA abundance and protein levels at 1, 2, 4 and 24 h were examined. While manganese superoxide dismutase (MnSOD), glutathione peroxidase (GSHPx) and catalase (CAT) activities were not significantly changed, copper-zinc superoxide dismutase (CuZnSOD) activity was reduced at all time points and this change correlated with a decrease in its protein content. CuZnSOD mRNA was increased at 1 and 24 h. GSHPx mRNA and protein levels were transiently decreased by 20 and 25% respectively at 2 h. MnSOD mRNA was not significantly changed, but its protein levels were significantly decreased at 1 h. Lipid peroxidation was increased transiently at 1, 2 and 4 h. A transient depression in antioxidant enzyme as well as transient increase in oxidative stress with a single dose of adriamycin may precede more sustained changes seen with the repeated administration of the drug and contribute to the development of cardiomyopathy and heart failure.