During the years 1990 to 1991, smears taken from the anal canal of 45 randomly selected homosexual males were studied. Several cytological criteria were used to study infection by human papillomavirus (HPV). The cytological study and an anoscopy was performed and a swab was taken for HPV-DNA hybridization, using labelled RNA probes for HPV-DNA: 6,11,16,18,31,33, and 35. In our study we observed the existence of a high proportion (9.5%) of inadequate smears that did not contain glandular cells and/or metaplasia. A sensitivity of 78% and a specificity of 72% was obtained. Sensitivity and specificity were 68% and 91%, respectively, when these criteria were restricted to the presence of koilocytes and/or dyskeratocytes. The high rate of occult infections obtained in our study lead us to suggest the simultaneous use of cytology, molecular hybridization, and anoscopy for suitable care of those patients with a high risk of contracting HPV infections of the anal canal.