Using carefully standardized test conditions and tandem pairs of cells of Nitella flexilis, the influx of 14C (added as H14CO3− and transnodal transport were studied under various pressure gradients applied across the node up to ΔP=± 2·5 bar. When mannitol was used as the osmoticum, influx was found to increase only when the mannitol solution was around the cell proximal to the feed. 14C was transported across the node to the distal cell, probably as 14C-photosynthate products, even against a pressure gradient of 2 bars or more, as was 36Cl− and 32P. The % transported in general decreased with increasing ΔP, whether assisted or opposed by added pressure. It was unchanged by the presence of mannitol at the node and was essentially the same whether the pressure gradient was produced by direct pressure or by use of the osmoticum. Transnodal transport of 14C products is almost certainly via plasmodesmata and appears to be largely by an active mechanism. In absolute amounts it is the same whether the pressure gradient assists or opposes flow. Valving is evident at the node, increasing the resistance to transport as the pressure gradient increases whether 14C(as HCO3−), 42K+ (as KCl), 36Cl− (as NaCl) or 32P (as Na3PO4) are used to detect it. The mechanism of movement of K+ across the node differs from that of photosynthate products.