Growth parameters of 3 strains of the Lactobacillus casei and paracasei bacteria were detd. In particular, biomass prodn., no. of cells, duration of adaptive phase, proper speed of growth, dynamics of growth, and Se accumulation in cells were measured. All strains used fulfil the requirements for probiotic bacteria. The probiotic Se-contg. prepns. were recommended as a new food component used for enrichment of fodders and food-stuffs for animals.