The aims of the study were to find the prevalence of cervical Chlamydia trachomatis infection in women attending for a speculum examination, to examine possible risk factors, and to see if we could develop a rational policy for testing for chlamydia in our deprived inner London practice. During 18 months 409 women aged 17-45 (mean 28) who attended for a cervical smear or vaginal examination were tested for chlamydia using the direct immunofluorescent test. They were assessed for possible risk factors: age less than 25, more than one sexual partner in the previous 3 months, sexual contact with men with urethritis, past history of chlamydia infection, purulent vaginal discharge, cervicitis and abnormal cervical cytology. Thirty-six women (8.8%) were chlamydia positive. Chlamydia infection was significantly associated with the presence of purulent vaginal discharge or an inflammatory cervical smear. In view of the prevalence of chlamydial cervicitis, the lack of symptoms and signs, and the potential consequences of untreated infection, ideally all young women in this population should be offered screening when they attend for a speculum examination. If this is not practical, chlamydia testing might be offered to women thought to be in high-risk groups including those with purulent vaginal discharge or an inflammatory cervical smear.