Griffonia simplicifolia agglutinin (GSA) is a valuable histochemical tool in the identification of endothelium. In this study GSA labeled with fluorescein isothiocyanate (GSA-FITC) was used to purify cultures of murine cerebral microvascular endothelium. Cultures were stained with GSA-FITC, then sorted using a fluorescence-activated cell sorter (FACS). GSA-positive endothelial cells were collected, re-cultured, and subsequently re-analyzed by FACS using GSA-FITC. Cultures that initially contained 80 +/- 3 to 89 +/- 3% (X +/- SE) GSA-positive cells were purified to 98 +/- 1% positivity. Immunohistochemistry with an anti-muscle-action antibody confirmed that FACS sorting of GSA-FITC-stained cells effectively removed contaminating smooth muscle cells from endothelial cell cultures. Viability, proliferation, and prostaglandin production of the cells was unaltered by lectin staining and FACS sorting. Thus, GSA-FITC can be used in conjunction with flow cytometry to enhance the purity of murine endothelial cell cultures without adversely affecting cell viability, growth, or metabolism.