A randomized trial of doxycycline versus amoxicillin was performed to treat mucopurulent cervicitis. Chlamydia trachomatis, the most common single agent associated with mucopurulent cervicitis, was isolated from 30 (47%) and Neisseria gonorrhoeae from five (8%) of 64 patients. Patients were followed up for 3 months, and the effect of treatment was assessed by clinical (presence of endocervical mucopus, cervicitis severity score, and number of polymorphonuclear leukocytes on Gram-stained smears of endocervical secretions) and microbiologic criteria. Doxycycline and amoxicillin were equally effective for treating chlamydial and nonchlamydial cervicitis. However, endocervical mucopus was still present in 18% of the patients in both treatment groups after 2 months and in 23% of the doxycycline group and 33% of the amoxicillin group after 3 months of therapy. The cause of persistent/recurrent mucopus after antimicrobial treatment was not explained by relapse or reinfection with Chlamydia trachomatis, Neisseria gonorrhoeae, genital mycoplasmas, or Gardnerella vaginalis, but persistence was associated with the degree of cervical ectopy.