The frequency and morphology of myoendothelial junctions occurring in human saphenous veins have been investigated. The junctions are mostly established via slender membrane projections. The junction slit is filled with a electron-dense material, sometimes forming shark-tooth-like configurations. The morphology of these heterocellular junctions is not compatible in all cases with gap junctions, tight junctions or desmosomes. The frequency of heterocellular junctions in endothelial cells of saphenous veins is estimated to be approximately 10 per cell, but their significance is not finally determined.