Endocervical specimens obtained by cytobrush and conventional cotton wool swabs from 90 women attending a genitourinary medicine clinic were compared for their efficiency in detecting chlamydial infection. Isolation of Chlamydia trachomatis and detection of the chlamydial lipopolysaccharide antigen were attempted on each specimen. Antigen was detected in 18% of cytobrush and 17% of swab specimens. The cytobrush proved less suitable than swabs for isolation because 8 cytobrush specimens (9%) were toxic to the McCoy cells. Toxicity was significantly associated with an infected endocervix (2P = 0.004). Cytobrush therefore appeared to have little advantage over the much cheaper alternative, the cotton wool swab.