The binding of concanavalin A to the plasmalemma of higher plants has been studied using protoplasts of two species. The lectin aggregates both tobacco (Nicotiana tabacum L.) leaf protoplasts and protoplasts prepared from a suspension cell culture of grapevine (Vitis vinifera L.). Differences in lectin binding have been investigated using concanavalin A conjugated to ferritin or bound to colloidal gold. Tobacco protoplasts exhibit continuous and saturated labelling of the plasmalemma surface with gold-concanavalin A mixtures. Vine protoplasts under the same conditions show a discontinuous and patchy distribution of label. These results are discussed in terms of a possible binding mechanism.