In the majority of women chlamydia infections remain asymptomatic but they may increase the risk for tubal factor subfertility. Pelvic inflammatory disease (PID) and its chronic sequelae are associated with chlamydial IgG antibody formation in serum, and a correlation between the height of antibody titres and the presence of tubal factor subfertility has been established. The predictive value of chlamydia antibody testing (CAT) is limited however. Several factors affecting sensitivity and specificity of CAT have been identified. Because it is assumed that the presence of chlamydial heat shock proteins (HSPs) may be indicative of chronic inflammation, chlamydial HSP60 antibody testing has been evaluated in its prediction of tubal factor subfertility.