Autosomal dominant polycystic kidney disease (ADPKD) is a common inherited disorder (incidence of 1 in 1,000), the cardinal manifestations of which are renal and liver cysts and intracranial aneurysm. The gene defective in the most common and severest form of ADPKD, PKD1, is broadly expressed and encodes a 4,302 amino acid plasma-membrane protein, polycystin-1 (PKD1)[1–3]. Despite detailed knowledge of the domain architecture for the majority of the PKD1 sequence (Figure 1), little is known of PKD1 function. Identification of PKD1 mutations has been hampered by the presence of numerous PKD1 homologues elsewhere on chromosome 16 [2] and in vitro expression of full-length PKD1 is yet to be reported. Here, we report the identification of three previously unrecognised domains in PKD1 that are likely to possess distinct carbohydrate-, lipidand protein-binding functions. These domains were identified using PSIBLAST database searches [4, 5] with an expect-value (E-value) inclusion threshold of E< 0.01. Independent evidence was provided using a generalised profile analysis method [6], in which the significances of findings were better than p< 0.01 in