Twenty Mycoplasma hominis strains isolated from colonized women and women with various urogenital infections were investigated for genetic and antigenic homogeneity by different methods. Restriction fragment length polymorphism analysis demonstrated heterogeneity for all strains, with one exception. Two strains sequentially isolated from one patient showed identical patterns. Otherwise, no clonal clustering could be detected within the strains isolated from either of the diagnostic groups. In contrast, SDS-PAGE analysis and the comparison of the immunoblot pattern revealed antigenic similarities of strains isolated from patients with bacterial vaginosis, chorioamnionitis, premature rupture of membranes and preterm delivery as well as endometritis but showed obvious differences in comparison to strains isolated from colonized women.