[en] In this review, low-dose levels for high- and low-LET radiation are defined to be <5 cGy and <20 cGy, respectively, and the data of various long-term mouse studies performed at Centro Casaccia's laboratories are considered especially on the analysis of the available results of the dose regions within 17 cGy for neutrons and 32 cGy for X-rays. Particularly, mouse studies are described on treatment with single doses of 1.5 MeV neutrons or 250-kVp X-rays, with fractionated or acute doses of fission neutrons, with in utero single doses of fission neutrons or 250-kVp X-rays and with single doses of fission neutrons in another mouse strain. In all cases the analysis object considered is the animal-at-risk and ovary and solid neoplasms are discussed. Data seem to reinforce the idea that at low doses the effectiveness of ionizing radiation is in practice very low in inducing neoplasms in the laboratory mouse. (K.H.)