Human papillomavirus (HPV) type 33 belongs to potentially oncogenic types in genital cancers, but its infection corresponds to an intermediate risk for progression towards malignancy. We studied by in situ hybridization with biotinylated probes the incidence of HPV 33 infection in a series of 106 skin lesions and 12 mucosal lesions from heart and renal transplant recipients, 34 skin lesions and 17 mucosal lesions from normal population. We have shown that skin lesions from both populations could harbor HPV 33. In transplant recipients, HPV 33 was identified in 12/77 premalignant and malignant lesions and one oral leukoplakia; in the normal population, HPV 33 was detected in 2/13 warts and 2/15 mucosal lesions. The analysis of in sial hybridization signal pattern of the 17 HPV 33 positive samples suggests that a strong viral DNA signal was uniformly distributed in the nuclei of positive cell foci in 11 cases and punctate signals were seen in the nuclei of dispersed cells of 6 skin biopsies. The significance of the presence of HPV 33 DNA in skin lesions is not clear; the hybridization signal pattern may be important, mainly in premalignant actinic keratodses of organ transplant recipients although other factors are most likely involved to change the epithelial environment.