Scorpion venoms contain different types of low molecular mass toxic peptides acting on ion channels. Many cDNAs and genomic genes encoding these toxins have been isolated and sequenced while the mechanisms of expression and regulation of scorpion toxins is not well studied yet. BmTXK beta, one of the four putative long-chain potassium channel toxins, is isolated from the cDNA library of the venom gland of Chinese scorpion BmK (Buthus martensii Karsch). It has an 886 bp intron located in the mature peptide while other scorpion toxins' introns are located in the signal peptide. The special genomic organization of BmTXK beta makes it a good object to study the mechanism of expression and regulation of scorpion toxins. With primers designed according to the already known sequence of BmTXK beta, its 5' and 3' flanking regions are cloned by the Vecttorette II Staorette Pack method and sequenced. Analysis of the sequence shows that another intron longer than 997 bp is located in the signal peptide region of BmTXK beta, which makes BmTXK beta different from all the other scorpion toxins that have no intron or only one intron in the signal peptide. The special genomic organization of BmTXK beta indicates that BmTXK beta is a new membership of long-chain potassium channel toxin.