Letter from Dr G. M. Atkin, Cutter, to Dr V. E. Mitchell, Leicester Royal Infirmary, regarding Koate HT 50R004 and Dr Mitchell's claim that this batch caused a patient to seroconvert to express Hepatitis B antigens. Dr Atkin suggested that there have been no other adverse reports about this batch of Koate HT and that the plasma that went into the batch was Hepatitis B antigen negative. Dr Atkin expressed that in conjunction with whole blood and platelets, they do not believe Koate HT to be the probable source of the patients' Hepatitis B.