The effects of two different keeping systems on the humoral immune response and productivity were compared for 80 laying hens, divided into four groups. Two groups, each of 20 hens, were kept on the ground and two were kept in cages. All the birds were immunised subcutaneously with human serum immunoglobulin G at a dose of 100 mug per injection. The immunisations were performed twice at 4-week intervals. The lipopeptide Pam(3)Cys-Ser-(Lys)(4) was used as an adjuvant at a dose of 0.25mg per injection in one group from each housing system. In the second group from each housing system, the hens were immunised without any adjuvant (antigen control groups). The mean egg yield was significantly higher in both the antigen control group and the adjuvant group, when laying hens were kept in cages. Total egg weight remained constant in bath of the housing systems. Keeping hens in cages resulted in higher mean specific antibody titres and mean immunoglobulin Y concentrations in the egg yolk.