A genomic fragment containing the coding exons of the chicken lysozyme gene (also known as hen egg lysozyme, HEL) was linked to a 600bp fragment of the rat insulin promoter and to the mouse H2-Kb transmembrane sequence (which included the extracellularspacer sequence, transmembrane segment, and cytoplasmic tail). The rat insulin promoter was used to direct expression of the inserted sequence specifically to pancreatic islet beta cells. Islets from mice carrying the transgene showed expression of chicken lysozyme by Western blot; spleen, thyroid, and thymus did not.