Intestinal tissue from rabbits heterozygous at one or both of the alpha-chain subclass loci, i.e., f or g, was examined with mixtures of rhodamine-labeled and fluorescein-labeled antibodies each directed against one of the allelic products of the f or g locus. Individual plasma cells were stained by only one fluorescent reagent and thus exhibited both allelic exclusion and sublcass exclusion. In contrast, the epithelial cells of the Lieberkükhn's glands sid not exhibit allelic exclusion. Studies with rabbits heterozygous at the f and g loci revealed that the ratio of the number of cells expressing maternal-type f cells to paternal-type f is equal to the ratio of the number of maternal-type g cells to paternal-type g cells. These data are used to suggest that the expression of each of the genes in the heavy chain chromosomal region of a particular allogroup is under the same control.