Antibiotics were given subcutaneously to female mice, colonized by mycoplasmas in the vagina and by others in the oropharynx. Mycoplasma pulmonis was eradicated from the vagina of 36 of 42 immunocompetent TO or BALB/c mice with oxytetracycline, and from 17 of 18 TO mice with lymecycline. Mycoplasma hominis was eradicated from the vagina of all of 18 immunocompetent BALB/c mice with oxytetracycline or tetracycline. Regarding oropharyngeal organisms, M. pulmonis was eradicated from only 20 of 42 TO or BALB/c mice with oxytetracycline and from none of 15 mice with lymecycline. However, Mycoplasma pneumoniae was eliminated from the oropharynx of eight of nine BALB/c mice with oxytetracycline. In contrast to the success in eradicating mycoplasmas from the vagina or oropharynx of immunocompetent BALB/c mice with oxytetracycline, no such effect was seen in nude BALB/c mice, indicating the importance of a competent immune system in conjunction with antibiotic treatment for eradication of these organisms.