Urethane-induced lung adenomas from adult BALB/c mice were explanted onto a plastic substratum and cultured in order to establish the epithelial cell strain NUL1. The cell strain exhibited a polygonal morphology with high nuclear to cytoplasmic ratio and osmiophilic lamellar bodies characteristic of lung adenoma cells. A reproducible large and small cell heterogeneity was preserved despite multiple cell cloning. NUL1 was malignant at all passage numbers tested exhibiting anchorage-independent growth and subcutaneous formation of carcinomas in immunesuppressed mice. The cell strain was diploid at low passage numbers and became pseudo-diploid with increasing passages.