The relationship between type 1 pilus structure and the mannose-sensitive adhesin was investigated by analysing the properties of an 11.2 kb fragment of DNA derived from the chromosomal pil region of a type 1 piliated uropathogenic strain of Escherichia coli. The recombinant plasmids pHA9 and pSJH9, containing the cloned fragment, conferred a mannose-sensitive haemagglutination (MSHA)-positive but non-piliated phenotype on recipient cells of ORN104. Most of the DNA sequences homologous to the pilA and hyp genes were not present in the 11.2 kb insert, and the genetic information necessary for MSHA in the absence of piliation spanned a 6.5 kb region of the cloned fragment. The polypeptides expressed by pSJH9 were examined in minicells and Tn1000 insertions in three genes encoding proteins of molecular weights 90 kD, 29 kD and 17 kD abolished the MSHA phenotype.