In this work, autoaggregation and factors involved in the autoaggregation ability of vaginal lactobacilli were studied. The autoaggregation ability of 28 lactobacilli strains was positive. The effects of various factors on autoaggregation were also evaluated. Lactobacillus jensenii A1, L. salivarius I1, and L. cellobiosus I3 showed higher autoaggregation in acidic conditions and lower autoaggregation in hot (70 and 85 degrees C), conditions. The L. salivarius I1 strain, which exhibited high autoaggregation activity, also showed good autoaggregation in pepsin, lipase, and sodium periodate, as well as under conditions of sonication and heat. The results of this study suggest that lactobacilli showing high autoaggregation may constitute an important host defense mechanism against infections as a probiotic.