Scanning electron microscopy (SEM) was used in this study to investigate the mechanism of association of cholera vibrios with the intestinal mucosa. For this purpose, the interactions of three virulent, wild type strains (CA401, P, and 3083) of Vibrio cholerae with intestinal segments of infant mice were compared. The results of previous studies by different investigators using the three strains separately and in different assay systems had led to differing conclusions concerning the mechanisms of association with the mucosa. In this study, observations by SEM of the infant mouse intestinal segments, previously incubated in suspensions of the organisms, revealed that all three strains preferentially associated with intestinal mucin. The vibrios associated poorly with the mucosal epithelial surface even in areas of the segments free of mucin or in segments washed to remove mucin prior to the assay. In each case, the vibrios associated better with the serosal surface than with the epithelial surface of the mucosa, but not to the degree that they associated with mucin on the mucosal surface. The major difference observed by SEM of the strains was the markedly greater association of strain 3083 with the serosal surface as compared to strains CA401 and P.