The barley (Hordeum vulgare) protein Zx gene (3283 bp) has been isolated and sequenced in its entirety. The predicted 398 amino acids (aa) of Zx are 70% identical to barley protein Z4 and show approx. 30% similarity to the animal members of the serpin superfamily. Zx has an Arg-Ser as the putative reactive site. The Zx gene is interrupted by a 971 bp intron located at a position identical to that in Z4. The 5′ and 3′ noncoding regions as well as the intron show no pronounced sequence similarity to the Z4 gene or other plant genes.