Summary Living cells of Euglena gracilis were exposed to ferritin-coupled concanavalin A and the intracellular distribution of the opaque tracer was examined by electron microscopy. The conjugate entered 15–20% of the organisms and the lectin binding occurred around the chloroplasts and within the chromosomes. A possible relationship between the lectin-chromosome interaction and the mitogenic activity exerted by concanavalin A on Euglena cells is discussed.