Studies designed to assess the histomorphological, ultrastructural histochemical and biochemical characteristics of altered cell types in pulmonary neoplasms of mice are currently underway. Over the past year, we have evaluated the gross histomorphological and ultrastructural characteristics of pulmonary tumors in aged Strain A mice in an attempt to further clarify differences between neoplastic and nonneoplastic lung tissue using conventional light and electron microscopy. Automated lectin staining, two dimensional gel electrophoresis and gold-labeling electron microscopic techniques to evaluate glycoconjugate composition of nonneoplastic versus neoplastic cells, and malignant versus benign tumors, are in progress. Additional in vitro studies to characterize the histogenesis of mouse lung tumors are underway.