Six ClC-type chloride channel genes have been identified in Caenorhabditis elegans, termed clh-1 through clh-6. cDNA sequences from these genes suggest that clh-2, clh-3, and clh-4 may code for multiple channel variants, bringing the total to at least nine channel types in this nematode. Promoter-driven green fluorescent protein (GFP) expression in transgenic animals indicates that the protein CLH-5 is expressed ubiquitously, CLH-6 is expressed mainly in nonneuronal cells, and the remaining isoforms vary from those restricted to a single cell to those expressed in over a dozen cells of the nematode. In an Sf9 cell expression system, recombinant CLH-2b, CLH-4b, and CLH-5 did not form functional plasma membrane channels. In contrast, both CLH-1 and CLH-3b produced strong, inward-rectifying chloride currents similar to those arising from mammalian ClC2, but which operate over different voltage ranges. Our demonstration of multiple CLH protein variants and comparison of expression patterns among the clh gene family provides a framework, in combination with the electrical properties of the recombinant channels, to further examine the physiology and cell-specific role each isoform plays in this simple model system.