The periodontal status of three groups of women: pregnant, taking oral contraceptives, and nonpregnant, were evaluated clinically and microbiologically for changes in their gingiva and any corresponding changes in the subgingival microbial plaque, specifically the percentage of Fusobacterium species and Bacteroides species. Overall, the women had relatively good gingival health. However, statistically significant increased scores were observed in the Gingival Index and the gingival crevicular fluid flow in the pregnant group compared with the nonpregnant group. The most dramatic microbial changes were the increased proportions of Bacteroides species both in the pregnant group and the group taking oral contraceptives over the nonpregnant group. Increased female sex hormones substituting for the naphthaquinone requirement of certain Bacteroides were most likely responsible for this increase. No statistically significant clinical difference was noted between the group taking oral contraceptives and the nonpregnant group, although a 16-fold increase in Bacteroides species was observed in the group taking oral contraceptives.