THE genelin-11 is required for the asymmetric division of a vulval precursor cell type in the nematode Caenorhabditis elegans. Putative lin-11 complementary DNAs were sequenced and found to encode a protein that contains both a homeodomain and two tandem copies of a novel cysteine-rich motif: C-X²-C-X_17–19-H-X₂-C-X₂-C-X₂-C-X_7–11-(C)-X⁸-C. Two tandem copies of this motif are also present amino-terminal to the homeodomains in the proteins encoded by the genes mec-3, which is required for C. elegans touch neuron differentiation¹, and isl-1, which encodes a rat insulin I gene enhancer-binding protein². The arrangement of cysteine residues in this motif, referred to as LIM (for lin-11 isl-1 mec-3), suggests that this region is a metal-binding domain. The presence in these three proteins of both a potential metal-binding domain and a homeodomain distinguishes them from previously characterized proteins.