Although there have been some studies of the relation between behavior and mitogen-induced lymphocyte proliferation and immunoglobulin synthesis, few data are available about the effect of behavior on specific lymphokine production. In this study, we describe the effect of social and territorial behaviors on interferon-γ (IFN-γ) production by concanavalin A-stimulated peripheral blood mononuclear cells (PBMCs) in pairs of socially naive male rabbits living in a seminatural open-air environment. We also assayed PBMC glucocorticoid receptors (GcRs) and plasma corticosterone (C). Three groups of behaviors were identified: agonistic (Mount and Follow), affiliative (Groom) and territorial (Mark and Dig). Mount was correlated with Follow, while Mark was correlated with Dig. Groom was correlated with all the other behaviors. Groom, Mark, Mount and Follow were all positively correlated with PBMC GcRs. Groom and PBMC GcRs were each negatively correlated with plasma C. The two rabbits in each pair could be distinguished in terms of territorial behavior, since one animal always had a higher score. The animals with the higher level of territorial behavior within the pairs exhibited a significant increase in IFN-γ production at the end of the experimental period. They also showed a positive correlation between the percentage variations of IFN-y production and PBMC GcRs. It is suggested that social factors, especially territorial behavior, affect adrenocortical activity and IFN-γ production.