Although the experimental data presented in this article refer to steel of a specific composition (15Kh3MFA), the analysis made of the rules established in the test makes it possible to assume that they are general for a wide range of hardened and tempered low-alloy carbon steels with an original structure of dislocation (lath) martensite. Included in such rules are the following. 1. The basic factor regulating radiation embrittlement and radiation strengthening is the concentration of dissolved carbon (or nitrogen), the atoms of which play the role of traps for point defects, promoting an increase in the concentration of complex radiation defects. 2. In low-alloy steels with a significant concentration of dissolved interstitial atoms (carbon, nitrogen) the role of the density of dislocations as natural outlets regulating the formation of radiation defects is leveled. As a result the change in dislocation density over wide limits (one or two orders of magnitude) does not influence the characteristics of radiation embrittlement (Δ) and radiation strengthening (Δσ0.2). 3. Carbide transformations influence radiation effects in steel in two ways. On the one hand, as a result of carbide transformations there is a change in the concentration of dissolved carbon, which in the final analysis influences the concentration of complex radiation defects, and, on the other, with development of carbide transformations there is a change in the extent of the portions of large angle boundaries free from carbide phase and, as a consequence of this, in the degree of influence of neutron irradiation on the large angle boundaries.