Problems associated with the use of the lecithovitellin (LV) reaction for typing strains of Clostridium oedematiens have been defined and and investigated. The haemolysins of the various types of the organism were studied with particular reference to their application to serological neutralisation tests. A haemolysin (HL) neutralisation test has been developed with human red cells as the substrate; the test is recommended for use in parallel with the LV test system in typing procedures. The HL test is more sensitive than the LV test and is of particular value in identifying type-B strains, which frequently produce inadequate amounts of the β-antigen for detection in LV tests with unconcentrated culture products.