Using NaH 14CO3 (0.1 to 3.0 mol m −3) fed to 5.0 mm of an internodal cell of Nitella flexilis in artificial pond water at pH 6.8 and 19–25 °C, we have found that the carbohydrates (lactose, xylose, mannose, galactoseand sucrose) are formed by photo-assimilation from 14C-DIC (dissolved organic carbon) in 1 h and are carried in the cytoplasm with amino acids (glutamine and alanine in particular) to the node attached to a tandem internodal cell. These small sacchandes and some amino acids passed, apparently unchanged, across the node into the sink cell. Influx of DIC was highly sensitive to inhibitors of photosystems I and II (at concentrations around 1.0 mol m−3) and to uncouplers of phosphorylation. Most influx inhibitors, except for NaN3, also reduced % transnodal transport. NH4+ (1.0 to 5.0 mol m−3) appeared to reduce % transport in light (but not in dark) with much less effect on influx. Dinitrophenol and Na citrate (at pH 8.2) also strongly reduced apparent % transport without altering cytoplasmic streaming rates. Some of the apparent reduction of transport could be due to an alteration of metabolism or of sequestering in the feed cell, but with NH4+ the latter was not detectable. Our findings support the hypothesis that transnodal transport, including that via the plasmodesmata, is at least partly ‘active’ and requires metabolic energy to sustain it.