We compared lectin staining patterns to cell population densities, as determined by morphological criteria in rat airways. Eight lectins were studied: Griffonia simplicifolia I isolectin B4 (GSI-B4), Arachis hypogaea (PNA), Wisteria floribunda (WFA), Glycine maximus (SBA), Dolichos biflorus (DBA), Helix pomatia (HPA), Ulex europaeus (UEA-1), and Maclura pomifera (MPA). Two of the lectins strongly stained morphologically distinct cell subpopulations. GSI-B4 stained basal cells, and MPA stained non-ciliated bronchiolar (Clara) cells. The specificity and sensitivity of GSI-B4 as a marker for basal cells was examined. In the trachea, 35% of all cells were GSI-B4 positive; 84% of these were basal cells, 7% were unidentified cells, 5% were serous/mucous cells, and 4% were ciliated, brush, or inflammatory cells. Comparison to cell population density data strongly suggested that all basal cells were GSI-B4 positive. The segmental bronchus was a transitional area; GSI-B4 positive basal cells were present in the region closest to the lobar bronchus but were absent in the distal region; instead, MPA-positive Clara cells appeared. When dissociated tracheal cells were obtained by pronase digestion, 43% were GSI-B4 positive. These results show that GSI-B4 is a sensitive and relatively specific marker for basal cells in the rat trachea which can be used to study dissociated epithelial cells.