Twenty different antigens have been detected on bovine lymphocytes. Family studies suggested that 19 of the antigens were under the control of two closely-linked loci. The remaining antigen was apparently coded for by an independent locus. The distribution of the antigens in the population also suggested that three loci control the expression of lymphocyte antigens. A co-capping study on two antigens which were inherited together on one haplotype showed that these antigens were expressed on different molecules on the lymphocyte membrane, providing further evidence for the existence of two linked loci.