Investigations on immune suppression and reconstitution of immune functions dependent on the presence of physiological microflora allow us to conclude that symbiotic microorganisms such as Lactobacillus sp. are essential for adequate activity of the defense system in humans. In addition to their beneficial influence on the intestinal microbial balance, these microorganisms exert a variety of immunomodulatory effects on the host immune system. On the other hand, immunostimulatory animal-derived substances rich in alkylglycerols have been shown to enhance lactic acid bacteria proliferation. Therefore, the aim of the present study was to evaluate the effects on murine humoral response of the combined administration of lyophilized combination of three lactic acid bacteria: L. acidophilus, L. bulgaricus and Bifidobacterium bifidum together with alkylglycerol-rich shark liver oil. The lactic acid bacteria mixture induced markedly stronger enhancement of the humoral response than alkylglycerols did. A significant synergistic stimulatory effect of lactic acid bacteria and alkylglycerols was observed in both treatment schedules: post-as well as in preimmunization with sheep red blood cells. However, their concomitant administration exerted stronger immunomodulatory effect than did the alternative route of treatment.