A study was made of the contribution of the cytobrush to determining the composition of the cervical smear. From a population of women screened in The Netherlands in 1987, 733 women were selected whose smears for the second time in a row lacked endocervical cells. Note was made of method of contraception, age of the woman, and day of the menstrual cycle. A control group was formed of women whose smears contained endocervical cells. Highly significant differences were found in the results between the two groups. Two new samples were collected, one made with the modified wooden Ayre spatula, the other with the cytobrush from the research group. The number of smears containing endocervical cells increased from 44% (by spatula alone) to 79% (spatula plus cytobrush). The cytobrush alone produced a high percentage of unsatisfactory smears (17.5%) due to a low content of squamous epithelial cells. No differences could be observed in the rate of cellular atypia because of the small number of cases.