Effects of the bacterial immunostimulant, Lactobacillus casei YIT 0003 (viable), on hematology and blood chemistry in normal and full thickness burned mice were studied. The white blood cell counts in normal and burned mice pretreated with L. casei cells at an early period after the intraperitoneal or subcutaneous administration of the cells were higher than in untreated animals. Significant increases in the population of neutrophils occurred in both groups of mice, at this period. On the other hand, L. casei cells did not affect red blood cell counts, platelet counts, plasma components, enzyme activities and electrolytes.