The distribution of gamma delta T cells during different developmental stages of pig foetuses was studied using monoclonal antibodies directed against a ruminant WC1 antigen, a T-cell receptor (TCR) subset epitope, and pig Null T-cell antigen. Binding was revealed by the avidin/biotin/peroxidase technique on cryostat sections and flow cytometry analysis. The extrathymic origin of gamma delta T cells was confirmed: gamma delta T cells appeared in the liver, spleen and peripheral blood sooner than in the thymus. In the course of the second half of gestation, these T cells were found in the dermis and intestinal mucosal compartments which represented the predominant loci of gamma delta T cells after birth.