THE nomenclature of the non-flagellar filamentous appendages of bacteria is in a confused state and the need for clarification is increased by a renewal of interest brought about by findings that suggest that some types of these structures may play a part in bacterial conjugation1–4. The appendages were first clearly described and distinguished from flagella and extracellular slime by Houwink and van Iterson5, who called them “filaments”, an unspecific term which was also used by Brinton et al.6. The distinctive name, “fimbriae”, was proposed by Duguid et al.7 in 1955 and has since been adopted by most authors publishing work on the subject in Britain and elsewhere.