Two allotypes of rabbit secretory IgA have been identified with antisera obtained by cross-immunization of rabbits with secretory IgA. The two antisera, anti-t61 and anti-t62, each reacted by double diffusion analysis with secretory IgA from some but not all rabbits. Both anti-t61 and anti-t62 reacted with purified free secretory component obtained from whey. Thus, anti-t61 and anti-t62 are identifying allotypic specificities on secretory component. Genetic studies revealed that t61 and t62 are controlled by allelic genes at an autosomal locus. The t locus is not closely linked to the VHa, Cαf and Cαg (heavy chain) loci nor to the b (light chain) locus of immunoglobulins.