The in vitro attachment between Escherichia coli and the human spermatozoon was studied using transmission and scanning electron microscopy, and ultracytochemistry. Samples from estrogenized cervical mucus columns containing migrating spermatozoa revealed two types of contact areas: Type I corresponded to the interaction of the bacterial fimbriae with the spermatozoal surface, and Type II, to the intermingling of the eukaryotic and prokaryotic cell glycocalyx. In both types of associations, the attachment area was lanthanum positive and displayed glycoconjugates. These types of intercellular contacts could represent the morphological basis of a mechanism by which bacteria are attached to spermatozoa and are consequently transported to the upper female genital tract.