Polymerase chain reaction is a recently developed procedure to detect point mutations in human genomic DNA. The sensitivity and specificity of this technique which requires a very little amount of DNA, have allowed the large scale screening of tumors. The Authors report the detection of point mutations of Ha-ras gene at codon 12 in 12 basal cell carcinomas and 10 cutaneous squamous cell carcinomas by the use of polymerase chain reaction in paraffin-embedded tissue sections. The gene alteration was identified in 2 basaliomas whereas no squamous cell carcinoma showed point mutations. These results suggest that point mutations of Ha-ras gene do not represent a general activating mechanism in cutaneous epitheliomas.