A panel of monoclonal antibodies to bovine leukocyte differentiation molecules was used to evaluate peripheral blood and splenic lymphocytes from cattle of various ages. The major population of peripheral blood lymphocytes from neonatal calves was gamma delta T-cell receptor (TCR1) positive, as determined by TCR1-N12 expression. TCR1-N12+ lymphocytes were decreased in number in older calves, and were lowest in adult cattle. The major subpopulation of TCR1-N12+ cells from peripheral blood coexpressed WC1, but not BoCD2. A small subpopulation of peripheral blood TCR1-N12+ cells from cattle of all ages coexpressed BoCD2, but not WC1. The TCR1-N12+ BoCD2+ lymphocytes made up the largest TCR1-N12+ lymphocyte subpopulation in spleens of both calves and adults. The TCR1-N12+WC1+ splenic lymphocytes were present as a small population. The data indicate that two subpopulations of TCR1+ lymphocytes are present in cattle of all ages. These two subpopulations are differentially distributed between blood and spleen, with TCR1-N12+WC1+ lymphocytes predominating in blood, and TCR1-N12+BoCD2+ cells predominating in spleen.