AbstractDimethyl disulphide (DMDS), the main cause of brassica anaemia in ruminant animals, was determined in the blood of steers ingesting S‐methylcysteine sulphoxide (SMCO) present in leafy brassicas. Blood samples were treated with Zn and dilute phosphoric acid and the DMDS reduced to methanethiol which was determined by gas chromatography headspace analysis. DMDS levels increased as the intake of SMCO with the brassicas progressed. They were maximal at the haemolytic crisis; thereafter, with the appearance of young red cells or reticulocytes, they declined sharply, but again increased as the new cells matured. The distribution of DMDS was; red cell 85%, plasma 15%. The distribution reached equilibriumin vitroin about 2