Lipoic acid (LA-(SS), LA) and its reduced form - dihydrolipoic acid DHLA-(SH)2, DHLA) are synthesized mainly in the mammalian liver. In this study, we investigated in viti the inactivation of yeast aldehyde dehydrogenase (ALDH) by nitroglycerin (GTN) in the presence and absence of LA and DHLA. In vivo studies were performed to answer the question whether LA administered jointly with GTN for 8 days will affect the ALDH activity in the rat liver. The results indicated that in vito both LA and DHLA restored and protected ALDH activity against GTN-induced inactivation, while treatment of rats with LA and GTN in combination did not provide any protection against GTN-induced ALDH inhibition. In summary, the obtained results seem to confirm earlier reports indicating the differential effects of LA in vitio and in vivo.