The difficulties encountered in the surface growth of Clostridium oedematiens (CI.novyi) of types B and D were investigated. Best results were obtained when nutrient agar was enriched with human blood (33 per cent.) and supplemented with (i) iron filings sprinkled on the surface of a seeded plate, or (ii) a development of Moore's cysteine-dithiothreitol system incorporated in the medium. The growth-enhancing effects of these two systems were not identical; different degrees of enhancement were obtained with the two systems when test cultures of different ages were used.