For 260 consecutive patient visits by women to a clinic for sexually transmitted diseases, four cervical specimens were cultured in duplicate for detection of Chlamydia trachomatis. Sixty-one positive results were detected by at least one of the four specimens; the first two specimens detected 67-69% and the last two 80-82% of the 61 positives. The difference in these isolation rates is statistically significant (P = 0.003). Duplicate cultures of the same specimen did not significantly increase detection rates. A combination of two specimens could increase the number detected by 44.7% beyond the results of a single-specimen culture. Contamination rates were higher for the first two specimens. Routine cleaning of the cervical canal with a swab before the taking of specimens should reduce contamination and increase the probability of obtaining infected cells when they are present.