Samples of human endometrial carcinomas of ranging degree of histological differentiation, and normal endometrial tissues were screened for the presence of single site DNA mutations at codon 12 of the C-K-ras gene using oligonucleotide hybridisation of DNA amplified by the polymerase chain reaction (PCR). Two instances of base substitution were detected; one resulting in a GLY-ALA amino acid replacement in a well differentiated (grade 1) tumour and the second causing a GLY-CYS replacement in a poorly differentiated (grade 3 tumour). The small number of samples tested does not permit conclusions to be drawn with respect to correlations between DNA point mutations and the clinical features, age of patient, tumour receptor status and degree of histological differentiation grading.