Abstract: Twenty-four, 3-4 days old male calves were used in this study. All animals were clinically normal. They were weighed within 24 h of arrival and divided into 3 groups A-C matched for body weight. Group A (control) calves were given a basal diet containing a combination of whole pasteurized milk and reconstituted milk replacer. In group B, a commercial culture of L. acidophilus and L. plantarum was added to the basal diet. In group C a culture of L. acidophilus 27 sc was added to the basal diet. Serum total proteins, albumin and total globulins were comparable in all three groups as were the serum concentrations of urea, BUN and triglycerides. Serum inorganic constituents also showed no significant differences between the control and treated groups. A significant increase in serum Ig G concentration was recorded in the probiotic-supplemented groups, which also showed a significant increase in body weight at 5 weeks and during the entire experimental period.