AbstractIn 1941 the Water Pollution Research Laboratory of the Department of Scientific and Industrial Research was naked by the Ministry of Supply to advise on the treatment and disposal of waste waters from retting of flax at a number of factories in England and Scotland. When these factories were built it was thought that it would not be necessary to ret flax in this country during the war, and at most of the sites waste waters from the usual anaerobic processes of retting could not be disposed of without causing undue pollution. Later experience showed that some retting would be necessary.As a result of an investigation by the Water Pollution Research laboratory, n process of aerated retting has been developed from which there is normally no discharge of waste waters. Several methods were tested in small‐scale plant. Results of experiments with the most promising method in full‐scale retting tanks were satisfactory; plants for the retting of flax by the aerated process were therefore installed by the Minister of Supply at several factories, and arc now in operation.