The human CLCN6 gene contains a 167 bp exon that is optionally included or excluded in ClC-6 mRNAs. The corresponding region (3.4 kbp) of the human CLCN7 gene has now been cloned and sequenced. a comparison of the human CLCN1, CLCN5, CLCN6 and CLCN7 genes indicates that there is no homologue of the optional CLCN6 exon in the CLCN1, CLCN5 or CLCN7 genes, Thus, the CLCN6 type of alternative splicing and the ensuing structural diversity is not conserved within the CLC gene family. (C) 1998 Elsevier Science B.V.