Skin cancer is the most prevalent cancer in the white population worldwide. Basal cell carcinoma (BCC) is undoubtedly the most common malignant skin cancer and abundant human malignancy in general. UV radiation in sunlight is the major environmental factor causing skin cancer development as a result of DNA damage in which Polι is suggested to be involved. To test the activity of DNA polymerases, tumor cell extracts were used in primer extension assays. Electrophoresis of the reaction products was performed. Activity of Polι was measured as misincorporation of G opposite T template (MoGvA activity) by phospho-imager. To investigate the relationship between DNA damages and skin tumor development, we determined the error-prone DNA polymerase iota (Polι) activity in a group of patients with BCC. Here we show that the activity and content of Polι were much higher in human skin BCC cell extracts than in extracts of benign skin tumors. Moreover, unlike in non-malignant skin tumors, extracts of BCC were able to extend products of Polι activity. Among all the studied extracts of normal mouse organs, only testis cell extracts demonstrated the same ability. It may be suggested that the elevated level of the MoGvA activity and appearance of activity overcoming T-stop is associated with malignant transformation and might be used as a diagnostic marker of this skin pathology.