A fragment of a cut-1 like gene from the filarial nematode Brugia pahangi (designated Bp-cut-1) was isolated by PCR from genomic DNA. The sequence was used to design primers for use in RT-PCR and resulted in the isolation of a cDNA fragment from larvae in the process of the L3-L4 moult. Screening of a B. malayi genomic library identified a single clone, Bm-cut-1. Using primers designed from the Brugia sequences, semi-quantitative RT-PCR was carried out on 11 different life cycle stages chosen to cover periods around the moult and inter-moult periods. This analysis demonstrated that the cut-1 mRNA was most abundant preceding the moult, consistent with its function as a cuticular protein. Immuno-gold electron microscopy using an affinity purified antiserum raised to the highly conserved region of Ascaris CUT-1 confirmed that the protein was restricted to a tight band in the median layer of the cuticle. Despite the fact that no transcripts could be detected in mature adult worms by RT-PCR, immuno-gold microscopy revealed staining of the microfilarial cuticle within the uterus of the adult female worm, suggesting that other cut-1-like genes are present in Brugia.