Bacterial vaginosis is one of the most frequent infections during the woman's reproductive age. Lactobacilli normal flora is substituted by relatively elevated Gardnerella vaginalis (GV), anaerobic bacteroids, Mobiluncus and Mycoplasma. The purpose of this study is to perform a morphological analysis of possible mechanisms for adhesion and penetration of GV in the heterosexual couple, in squamous epithelium at vaginal wall, as well as in seminal fluid. Ten couples with positive GV culture with three to four days of abstinence, were studied. The women presented with at least three of the four Amsel's criteria. Samples were obtained from vaginal lateral walls and from seminal fluid; these were divided in two parts: 1. To realize cultures for GV. Ureaplasma urealyticum and Mycoplasma hominis; and 2. For an ultrastructural analysis. Samples were processed with common techniques for electronic microscopy. In vaginal cells, bacteria similar to GV free form fixed to plasmatic membrane and inside the cellular cytoplasm. In the seminal fluid there were found numerous urethral cells of desquamation, which presented, as well as in woman, free form bacteria, fixed to plasmatic membrane and inside the cytoplasm. In four cases, bacteria similar to Mycoplasma, were found; and one case with particles suggesting cytomegalovirus. It is concluded in this study that: 1. The male presents with urethral cells similar to vaginal "guide cells". 2. GV colonizes urethral epithelium in the male. 3. Male is capable of infecting and/or re-infecting the woman.