Two Types of Haemophilia (A⁺ and A⁻): A Study of 48 Cases

S ummary . The inhibitor‐neutralizing ability of plasma and Factor‐VIII concentrates from a group of 48 haemophilic patients and 30 normal persons has been studied. Factor‐VIII inhibitors were neutralized by the material from four of the haemophilic patients and all the normal subjects. The material from the larger group of 44 haemophilic patients showed no significant inhibitor‐neutralizing ability. The former group have been designated Haemophilia A + because of the presence of material antigenically related to Factor VIII, and the latter group Haemophilia A − because of the lack of such material.