Histological analysis of intestinal preparations from ApcMin/+, K-ras+/+ (n = 8) and ApcMin/+, K-rastmΔ4A/tmΔ4A (n = 7) mice with overt signs of neoplasia revealed that all tumours from both genotypes were adenomas of similar, mild to moderate, dysplasia, with no evidence of invasive carcinoma in any of them. The gene discussed is KRAS; the disease is invasive carcinoma.