For treating Chlamydia trachomatis cervical infection in pregnancy, the Centers for Disease Control guidelines recommend either erythromycin base or erythromycin ethylsuccinate. There is no alternate therapy. Because of compliance problems with erythromycin regimens due to gastrointestinal side effects, such an alternative is needed. For this reason, we compared, in an open trial, the efficacy and patient compliance of amoxicillin (500 mg three times a day for 7 days) with those of erythromycin base (500 mg four times a day for 7 days) in treating Ctrachomatiscervical infections during pregnancy. In the amoxicillin group, 63 of 64 women (98.4%) had negative cervical cultures after treatment, compared with 55 of 58 women (94.8%) treated with erythromycin base. Vertical transmission to the infants was assessed by culture and/or persistent or rising immunoglobulin G antichlamydial antibody. In the amoxicillin group, 37 of 39 infants (94.9%) had no evidence of chlamydial infection, compared with 32 of 36 infants (88.8%) in the erythromycin group. These differences were not significant. The frequency of side effects was higher with erythromycin base than with amoxicillin (15 versus 8%), although not significantly so. However, the frequency of stopping medication because of side effects was significantly higher with erythromycin base than with amoxicillin (13 versus 2%; P<.006). These results suggest that amoxicillin may be an acceptable alternative treatment for chlamydial infections in pregnancy.