OBJECTIVE: We sought (1) to determine whether interleukin 6 levels are increased in plasma and cervical secretions and endometrial tissue obtained from women with a clinical diagnosis of pelvic inflammatory disease, (2) to determine whether interleukin 6 levels in these sample sites reflected the clinical severity of acute infection, and (3) to determine whether interleukin 6 levels in endometrial tissue obtained from these women were higher in the presence of histologic endometritis. STUDY DESIGN: We performed a prospective pilot study on 20 women with a clinical diagnosis of pelvic inflammatory disease (patients) and then compared them with 20 women presenting to the gynecology clinic without pelvic complaints (control subjects). Interleukin 6 levels were measured by enzyme-linked immunologic testing in plasma, cervical secretions, and endometrial biopsy specimens. RESULTS: Cervical interleukin 6 levels were higher in patients than control subjects (median, 317 vs 111 pg/mL; P =.003). Among women with pelvic inflammatory disease, statistically significant positive correlations were noted between the clinical severity score and the erythrocyte sedimentation rate (r = 0.45; P =.04), the clinical severity score and the white blood cell count (r = 0.49; P =.03), the plasma interleukin 6 levels and the erythrocyte sedimentation rate (r = 0.55; P =.02), and the plasma interleukin 6 levels and the white blood cell count (r = 0.54, P =.01). Endometrial tissue interleukin 6 levels were also higher in patients with versus those without histologic endometritis (median, 427 vs 17 pg/mL; P =.004). CONCLUSION: In this pilot study interleukin 6 levels in cervical secretions were significantly higher in women with pelvic inflammatory disease versus those without pelvic inflammatory disease. In women with pelvic inflammatory disease, endometrial tissue samples with histologic evidence of endometritis were observed to have higher levels of interleukin 6. Interleukin 6 may be a useful adjunct to the clinical diagnosis of pelvic inflammatory disease.