We studied the ability of laboratory and clinical strains of Mycoplasma hominis to colonize the genital tract mucosa in BALB/c mice. Colonization with mycoplasma occurred only in mice receiving estrogen. Mycoplasma hominis strains obtained after 3-fold passage through the vaginal mucosa in mice and administered intravaginally in a dose of 0.5 x 10(8) CFU/ml caused infection in 100% animals. Inflammation in the lower genital tract was reduced by the 8th week after infection.