This International Standard specifies laboratory procedures for measuring the mineralization and nitrification of nitrogen by the soil microflora. For investigations of a basic or advisory nature, outline procedures are given for evaluation of the rates and extent of N-mineralization in soil or soils of known or unknown quality. For investigation of the potential toxicity of chemicals to N-mineralization in soils, a simple procedure is given which allows the impact of single chemicals assessed and provides a basis for comparison of the toxicities of different chemicals.