The increase in the absolute amount of nitrogen in oak litter decomposing in oak woodlands was investigated. The main sources of the added N were atmospheric precipitation, insect frass and plant material which fell from the tree canopy. Neither the soil fauna nor the soil microflora were important sources of N. A maximum of 25% of the inorganic nitrogenous compounds in the rain was taken up by the litter. This was equivalent to 1.3 kg of N per ha in the first 9 1/2 months of decomposition. In years when caterpillars were abundant in the tree canopy the N increase in the litter amounted to 6.6 kg/ha, the bulk of this being derived from caterpillar frass and other plant material which fell from the tree canopy as a result of insect attack. The addition of this nitrogen-rich material to the oak litter did not accelerate its decomposition significantly in the 1st year after leaf-fall.