OBJECTIVES: To identify Chlamydia trachomatis via polymerase chain reaction and a direct fluorescent antibodyassay in patients with vernal keratoconjunctivitis while comparing the efficacies of both tests for detectingChlamydia trachomatis in these conditions. METHODS: Conjunctival scraping samples were obtained from 177 patients who were divided into two groups: avernal keratoconjunctivitis group (group A) and a control group (group B). The polymerase chain reaction and adirect fluorescent antibody assay were performed. Sensitivity, specificity, receiver operating characteristic curves,and areas under the curve were calculated for both tests in groups A and B. Receiver operating characteristic curveswere plotted using a categorical variable with only two possible outcomes (positive and negative). RESULTS: Statistical analysis revealed a significant association between vernal keratoconjunctivitis and Chlamydia trachomatis infection detected by a direct fluorescent antibody assay with high sensitivity and specificity. Allpatients in group A with positive polymerase chain reactions also presented with positive direct fluorescentantibody assays. CONCLUSION: The association between vernal keratoconjunctivitis and Chlamydia trachomatis infection wasconfirmed by positive direct fluorescent antibody assays in 49.4% of vernal keratoconjunctivitis patients and bypositive polymerase chain reactions in 20% of these patients. The direct fluorescent antibody assay detectedChlamydia trachomatis in a higher number of patients than did the polymerase chain reaction. Although thediagnosis of trachoma is essentially clinical, the disease may not be detected in vernal keratoconjunctivitis patients.Due to the high frequency of chlamydial infection detected in patients with vernal keratoconjunctivitis, we suggestconsidering routine laboratory tests to detect Chlamydia trachomatis in patients with severe and refractory allergicdisease.