The dose-dependent effects of gamma-radiation on the leucocyte cultures L-41 has been investigated. Irradiation by the dose of 0.25 Gy stimulates the cell proliferation while that by the doses of 1.0 and 2.0 Gy inhibits this process. In this dose range the radiohormesis effects characterizing structural organization of the probed membranes have been also registered for fluorescence parameters. The zone of qualitative transition of response of the cell membranes to radiation is individual for various effects. The action of radiation in the doses of 0.25 and 0.50 Gy induces a decrease of ANS fluorescence intensity and a decrease of membrane protein immersion in the lipid bilayer of leukocyte membranes. The values of these parameters rise at the doses of 1.0 and 2.0 Gy that reflects different directions of structural changes in various membrane regions. The irradiation in the range of 0.25-1.0 Gy induces the increase of microviscosity in deep regions of membrane lipid matrix while at the dose 2.0 Gy it causes its decrease. Radioactive radiation does not change the membrane protein conformation of leukocytes and polarity of lipid bilayer hydrophobic zones as recorded by fluorescent methods used.