In treating a still limited material of observations on the content of nitrogen in precipitation, collected under the supervision of Dr Egnér of the Agricultural College at Uppsala, we have obtained some preliminary results, which may be summarized as follows: The concentration of NH4-N and NO3-N in precipitation is dependent upon the amount of precipitation previously fallen. A mathematical expression is given for the dependence of concentration on amount of precipitation fallen. With aid of this relation a computation has been made of the normal supply of nitrogen at Uppsala, using known normal frequencies of different amounts of precipitation. A pronounced dependence of the concentration on the character of the air mass has been found to exist. Thus the tropical air contains between 10 and 30 per cent greater amount of nitrogen than the polar air, and almost double the amount found in the arctic air. DOI: 10.1111/j.2153-3490.1952.tb00986.x