A theoretical investigation of the indirect effect of radiation on the DNA macromolecule in dilute aqueous solution has been performed. A combination of the Monte Carlo method and the model of Smoluchowski together with the knowledge of rate constants for ·OH radical reaction with DNA constituents and the detailed model of the DNA atomic structure allows us to calculate patterns of ·OH radical attack on DNA. These patterns depend on DNA strandedness (single or double), base sequence and DNA conformation (A-, B-, Z-DNA). The comparison of the calculated patterns with the experimental data on strand breakage induced by γ-radiolysis enables us to discuss the results obtained in term of molecular mechanisms of radiation induced damage. We can conclude: a) for B-DNA the variation in initial damage is mainly determined by the rate constant of the chemical reaction of ·OH radical with different DNA components together with their specific position in the structure (sequence), and b) base radicals contribute only slightly to the formation of frank strand breaks, but significantly to the formation of alkali revealed breaks in B-DNA in dilute aqueous solution. For A-DNA only small differences in its radiolysis, as compared to the B-DNA, are predicted. On the contrary, calculations predict substantial differences in the indirect effect of radiation on the Z-form of DNA.