Leucocyte ascorbic acid was estimated in patients with abnormal leucocyte states and other haematological disorders. Levels below the normal range were found in most cases of chronic myeloid leukaemia and chronic lymphatic leukaemia. Subnormal levels were found in more than a third of patients with acute leukaemias, lymphomas, glandular fever, myelofibrosis, and polycythaemia, and in the same proportion of patients receiving cytotoxic drugs, and also in those with a polymorph leucocytosis and those with purpura. Most patients with anaemia but a normal leucocyte count, and those with myelomatosis had normal levels. The majority of pregnant women tested had subnormal levels. In a wide variety of leucocyte disorders the leucocyte ascorbic acid may not be an accurate index of the body's Vitamin C status. The results also support the supposition that leucocyte ascorbic acid is mostly carried by normal mature polymorphs.