S u m m a ry. - The subject of the study was 20 cases of non-small-cell lung carcinomas, up to 3 cm in diameter, conventionally designed as minimal lung cancers removed in patients operated on at the N. N. Blokhin Cancer Research Centre, Russian Academy of Medical Sciences in 1986 to 2001. According to survival rates after surgery, the patients were divided into two groups: 1) those who died within the first two years; 2) those who were followed up for 3-5 years. Histological, histochemical, and immunohistochemical studies were performed. The expression of argyrophylic nucleolar organizer site proteins (Ag-NOS-proteins) that characterized the rate of cell proliferation (the duration of a cellular cycle) and the expression of Ki-67 antigen, which reflected the fraction of growth (the number of proliferating cells), were revealed in the tumor cells. Minimal lung cancers were found to be a heterogeneous group of neoplasms showing differences in both the rate of cell proliferation and the count of proliferating cells. The cell proliferation rate is a determinant of the clinical course of minimal lung cancers. Group 1 tumors characterized by the superexpression of Ag-NOS-proteins and, accordingly, the higher cell proliferation rate and the moderate count of proliferating cells had a poor prognosis even in the presence of Stage IA whereas Group 2 tumors with a large quantity of proliferating cells, but with the less rate of cell proliferation were characterized by a much better prognosis. The rate of cell proliferation (expression of Ag-NOS-proteins) and the count of proliferating cells (the expression of Ki-67 antigen) should be simultaneously studied to have more complete information on the proliferative potential of tumor cells and on the prediction of the course of neoplasms.