Our purpose was to determine whether Chlamydia trachomatis persists in tubal tissues from monkey pocket models of chlamydial salpingitis and tubal infertility and to relate its presence to disease progression and histopathologic mechanisms. In situ hybridization was used to detect Chlamydia deoxyribonucleic acid in a monkey pocket model of salpingitis and in the direct tubal inoculation monkey model of tubal infertility. Results were correlated with culture and immunocytochemistry results and histopathologic characteristics. Chlamydia deoxyribonucleic acid was detected in the mucosa, submucosa, and deep tissues in the pocket model. In addition, it was present in peritubal adhesions from the direct inoculation model. Deoxyribonucleic acid was found at sites of inflammation and when culture and immunocytochemistry studies were negative. The presence of Chlamydia trachomatis deoxyribonucleic acid at sites of inflammation and tissue damage in monkey models of chlamydial salpingitis and tubal infertility suggests that Chlamydia persists and may be directly involved in the stimulation of the immune-mediated tissue destruction associated with Chlamydia trachomatis infections.