The objective of this study was to evaluate the effect of HMB on selected parameters of the humoral immunity in calves. The experiment was performed on 14 calves aged 30 +/- 2 days, divided into two equal groups of control (group K) and experimental (group H) animals. The feed administered to the experimental calves was supplemented with HMB at 40 mg/kg BW, whereas the control calves were administered standard farm-made feed without supplementation. Blood was sampled from the jugular vein immediately before the experiment (day 0) and on experimental days 15, 30 and 60 to determine the following immunological parameters: total protein levels, gammaglobulin levels, lysozyme activity and ceruloplasmin activity. An analysis of the results obtained revealed a significant increase (p < 0.05; p < 0.01; p < 0.001 respectively) in gammaglobulin levels and lysozyme activity throughout the entire experimental period, an increase (p < 0.05; p < 0.01 respectively) in ceruloplasmin activity on experimental days 15 and 30, but no changes in serum total protein levels of calves administered HMB as compared to those found in the control group.