Supernatant of rat heart homogenates obtained by centrifugation at 700 X g for 10 min, incubated in the presence of ethanol (25 and 50 mM) and glucose (10 mM) were found to oxidize ethanol to acetaldehyde (AcH) in such a way that after 60 minutes of incubation around 5 to 8 nmole per mg of protein were recovered. The addition of glucose oxidase (5 micrograms/ml), a known hydrogen peroxide generator system, to the incubation medium, significantly increased by about ten times the recovery of acetaldehyde. On the opposite, the presence of 3-amino-1,2,4-triazole (10 to 40 mM), a known catalase inhibitor, induced a concentration dependent reduction of the amount of AcH recovered during incubation even in presence of glucose oxidase. These findings support the idea that a catalase mediated oxidation of ethanol is acting in rat heart homogenates. AcH content of a medium in which rat heart homogenates were incubated in the presence of NAD (0.7 mM) decreased by 87% at 60 minutes. This effect was not observed in the absence of NAD or in the simultaneous presence of NAD 0.7 mM and disulfiram 30 mM. This fact is consistent with an NAD dependent disposal of AcH by a DS sensitive enzyme.