Caenorhabditis elegans is an ideal model system for the study of extracellular matrix biology as the C. elegans genome contains approximately 177 collagen genes, involved in the cuticle, basement membrane and other matrices. However, the proteins responsible for organising these collagens and linking them to cells are not known. In human extracellular matrices, a number of human collagen-binding proteins and collagen receptors contain VWFA domains. These are 200 amino acid modules which are directly responsible for collagen-binding function through a conserved mechanism. VWFA domain proteins of C. elegans are therefore candidates for collagen binding and organising proteins and we have been studying them to determine their role in C. elegans extracellular matrix biology. Here we report the findings for two genes, M01E10.2 and R10H10.3 M01E10.2: 5' and 3' RACE and RT-PCR showed the gene structure to be as follows; leader sequence, VWFA domain, cuticulin/ZP domain, transmembrane region and cytoplasmic tail. This differes from the predicted sequence, which gives an additional mucin-like domain detween the N-terminus and the VWFA domain. RT-PCR using cDNA from 2 hr intervals across the life cycle showed expression peaking at the inter-moult stages, similar to that seen for cuticle collagens. RNAi in N2 worms gave no apparent phenotype, but RNAi in daf-2 strain gave dumpy adults. This effect was restricted to daf-2 as other daf strains did not produce dumpy adults. M01E10.2 therefore appears to be a cuticle component. Significantly, untreated daf-2 adults are longer than N2s, suggesting that the daf-2 adult may synthesise different cuticle components to the N2 adult. These observations provide a direct link between the daf pathway and cuticle synthesis and provide an opportunity to examine this in detail. R10H10.3: This gene has the following structure; leader sequence, CUB domain and VWFA domain. RT-PCR showed that the gene is expressed constitutively across the life cycle. Transgenic worms carrying a promoter-GFP gene fusion showed that the gene is expressed in the intestine, and that expression is highter in males than hermaphrodites. This may be due to the presence of male-specific gene enhancers or sex-related differences in the intestine. R10H10.3 could be involved either in the assembly of intestinal epithelium basement membrane or in the assembly of the intestinal glycocalyx. The characterisation of these two genes shows that both probably form part of the extracellular matrix; however, their precise functions are likely to be quite different. This exemplifies the diverse roles that homologous protein modules can evolve to fulfil, and indicates that similarity at the sequence level does not always imply a straightforward similarity of function.