The disappearance of leaf litter in fresh water was studied in the River Thames. Three types of leaf litter were chosen: oak (Quercus robur L.), sycamore (Acer pseudoplatanus L.) and willow (Salix spp.). The oak litter disappeared more slowly than the two other kinds, but by the end of a year almost all the litter would have disappeared. The presence or absence of a normal benthic invertebrate fauna did not influence disappearance. The disappearance was caused principally by microorganisms. There were significant increases in the nitrogen content of the litter between the first and third months of the experiment. These increases must have been caused by absorption of nitrogen from the environment and are probably associated with an active microbial community living in or on the litter. The input of leaf into the Thames was 1.59 kg/m of shoreline/year, and 23.2 g/m2 of water surface/year. The energy input from litter into the Thames was a very low proportion of the population metabolism of fish, but the nitrogen input could have been an important element in the economy of the river.