Detection of Ki-ras mutations is one possible modality for diagnosis of human neoplasms, particularly of the gastrointestinal tract. Little is known about the protein expression levels of ras p21. Here we show a semi-quantitative analysis of mutated ras p21 in protein extracts from pancreatic and cholangiocarcinoma cell lines and from tumor tissues. Comparison with DNA sequencing data confirmed the specificity of the ELISA-mediated mutation analysis. Epithelial cell content from stroma rich tissues was estimated by measuring the CK 8, 18 and 19 concentration in protein extracts from tissue samples comparing this with the average keratin content in extracts from 21 GI-carcinoma cell lines. The combination of both tests allowed the analysis of the ras p21 content of tissues with as little as 5% tumor cell content.