Cell recognition and morphogenetic aggregation of embryonic cells into tissues are mediated by specific macromolecules in the cell surface (cell-aggregating factors). A factor specific for embryonic neural retina cells was demonstrated; its synthesis is required for histotypic reaggregation of retina cell suspensions. We show that proflavine (3,6-diaminoacridine) preferentially and reversibly suppresses production of the cell-aggregating factor and thereby inhibits normal cell reaggregation. If such proflavine-treated retina cells are exogenously supplied with the retina-specific factor, they reaggregate. The selectivity of these effects supports the postulated significance of specific cell-surface components in cell association into tissues; the results indicate that proflavine may be a useful molecular probe for studying formation of specific cell-surface components and their role in various cell interactions.