OBJECTIVE To identify the incidence of positive assays for direct antigen detection of Chlamydia trachomatis in oral contraceptive (OC) users with and without intermenstrual spotting and in women seeking contraception. METHODS We studied 65 women who had used OCs for more than 3 months and who presented with intermenstrual spotting for which no readily demonstrable cause could be identified. They were compared with 65 matched controls who were taking OCs without intermenstrual spotting and who had chlamydia testing because of one or more risk factors, and 65 matched controls seeking contraception. The incidence of positive tests for each group was compared by chi 2 test for independence using the Yates formula. The strength of the relationship was analyzed by determining the Craemer phi coefficient. RESULTS Nineteen of the 65 women (29.2%) taking OCs for more than 3 months and experiencing bleeding had positive tests, in contrast to seven of 65 matched controls (10.7%) who were also on OCs and who had had chlamydia testing because of vaginitis or new or multiple sexual consorts, and four of 65 women (6.1%) who were screened for C trachomatis before initiation of contraception. The significance level for the chi 2 statistic was P < .01. CONCLUSIONS Intermenstrual bleeding in women previously well regulated on OCs appears to be an added marker for chlamydial infection.