A medium containing 0.1% yeast extract (Difco) in addition to sucrose, inorganic salts, and chelated iron supported saprophytic growth of Melampsora lini (Pers.) Lév., race No. 3. Cultures were started with sterile uredospores from rust-infected flax tissue cultures and were maintained for over 5 months through up to eight transfers. In some aging parts of living mycelial cultures, single one-celled teliospores were formed on aerial hyphae, and in other parts composed of dense masses of firm, small cells, clusters of uredospore-like structures were found. Growth and survival of mycelium were better when 4% sucrose was used instead of glucose, and when 500 mg/l of K2HPO4 was present in addition to the routinely used potassium monophosphate. Spore production was increased by raising the yeast extract concentration to 0.2%.