Probiotic bacteria have been used in human nutrition for centuries and are now attracting more attention. In order to examine the immunological aspects of probiotic consumption, Lactobacillus rhamnosus LA68 was orally administrated using gavage to healthy C57BL/6 mice. After one month splenocytes were isolated, and analysed by flow cytometry. The magnitude of splenocyte proliferation upon stimulation with lipopolysaccharide and peptidoglycan and cytokine levels (IFN-γ, IL-6, IL-10 and IL-17) was assessed. Cytokine levels in the serum were also analysed. Oral application of strain LA68 leads to a significant decrease of CD3+, CD25+ and CD19+ cells, and an increase of CD11b+ and CD16/CD32+ positive cell populations in the mouse spleen. Increased sensitivity to stimulation through proliferation and IL-6 secretion was detected. Increased serum IFN-γ and decreased IL-10 levels were found. Our results show increased responsiveness of splenocytes, activation of the Th1 type of immune response, and a shift of leucocyte populations towards monocyte/granulocyte populations.