The distribution of concanavalin A (Con A) surface receptors and cytoplasmic actin in the same cell was studied in monolayer cultures of 2 odontogenic epithelial cells of different developmental age and in ecto-mesenchymal cells derived from the same tooth germ. Con A receptors were demonstrated by fluorescein-isothiocyanate-labelled Con A (FITC-Con A) and cytoplasmic actin by a specific anti-actin autoantibody (AAA) traced with a rhodamine-labelled goat anti-human globulin (R-AHG). All 3 cell types, incubated with FITC-Con A at 37 degrees C for increasing time periods, showed progressive changes in staining patterns from clusters, caps to perinuclear globules. Capping was seen in the majority of immature epithelial cells at 120--180 min, in cells of more mature epithelium at 180--240 min and in ecto-mesenchymal cells at 240--360 min. Binding of FITC-Con A to cell surfaces resulted in sequential changes in AAA staining from filamentous to an aggregated or diffuse pattern, co-capping of aggregated or diffusely stained areas with those capped by FITC-Con A, presence of aggregated or diffusely stained areas in sites similar to the perinuclear globules stained by FITC-Con A, to final re-emergence of filamentous staining. Prior treatment of cells with cytochalasin B or colchicine promoted capping in epithelial but not in ecto-mesenchymal cells while presence of either drug throughout the staining procedure inhibited capping. The results show that Con A receptors are more mobile in epithelial compared to ecto-mesenchymal cells and in immature epithelial cells compared to their more mature counterparts, and that binding and mobility of Con A receptors on the cell surface is associated with redistribution of cytoplasmic actin. The cytochalasin B and colchicine experiments suggest that both microfilaments and microtubules may have synergistic roles in the opposing functions of receptor anchorage and mobility, and that the relative receptor immobility of ectomesenchymal compared to epithelial cells may be attributed to firmer receptor anchorage to the cytoskeleton.