The cardio- and neuroprotective effect of the pyridoindole stobadine (S) is conditioned mainly by its good radical scavenging properties. It has been showed by EPR experiment, that the ultimate product of the reaction of stobadine with hydroxyl radical is the nitroxyl radical. However, for the unsaturated dehydrostobadine (DHS) the ultimate product was not experimentally determined, although its reactivity with a hydroxyl radical has been detected. Using the quantum chemical method AM1 we calculated the physico-chemical properties of S, DHS and their radicals. For the stobadine alone, the corresponding radical was formed by removing the H* from the NH group of indol, while in the case of DHS we removed the CH3* from the nitrogen in pyridine ring. For S and DHS we calculated the differences in the energies between the parent molecules and the corresponding radicals as well as the spin distributions for the radicals. The results confirmed the differences in the reactivities of S and DHS.