Cerato-ulmin (CU) is a low molecular weight hydrophobin protein secreted at high levels in vitro by the highly aggressive Dutch elm disease pathogen, O. novo-ulmi, but at much lower levels by the less aggressive O. ulmi. The recent discovery of an endemic Dutch elm disease fungus in the Himalayas, Ophiostoma himal-ulmi, which is a separate species from O. ulmi and O. novo-ulmi, yet like O. novo-ulmi produces high levels of CU in vitro, suggested that O. novo-ulmi may have acquired its cu gene from O. himal-ulmi. To investigate this possibility we have compared the nucleotide sequences of the cu gene isolates of O. himal-ulmi with those of O. ulmi and of the EAN and NAN races of O. novo-ulmi. Alignments of nucleotide sequences and their derived amino acid sequences are presented, allowing estimations of evolutionary relationships to be made. These comparisons indicate that the cu gene of O. himal-ulmi is less closely related to the cu gene of either O. ulmi or O. novo-ulmi than the cu gene of O. novo-ulmi is to that of O. ulmi; hence the cu gene of O. novo-ulmi is unlikely to have been acquired recently from O. himal-ulmi.