When the intrauterine contraceptive device user group was subdivided into copper users and Lippes Loop device users, a significantly lower geometric mean serum antibody titer among copper intrauterine contraceptive device users was detected. The odds ratio estimates for past chlamydial exposure (>or = 1:64 immunoglobulin G,>or = 1:128 immunoglobulin G) in users of noncopper versus copper intrauterine contraceptive devices were 9.1 (95% confidence interval 1.9 to 43.0) and 10.5 (95% confidence interval 1