The sensitivities of dot blot hybridisation and in situ filter hybridisation for the detection of HPV DNA were compared. Dot blot hybridisation was 10-50 times more sensitive than in situ filter hybridisation in detecting HPV 16 DNA in the cervical cancer cell lines SiHa and CaSki. Cervical smears collected from 51 women with a history of one or more abnormal cervical smears were tested by both hybridisation techniques for the presence of HPV 16 DNA; 11 were positive in the in situ filter hybridisation, 35 in the dot blot hybridisation. Thirty-five cervical biopsies available from this group of 51 women were processed for dot blot hybridisation. In 30 of the 35 cases the results of this hybridisation corresponded with the results of the dot blot hybridisation on the smears.