Legal resolution of the liability of a supplier of a useful and desirable product which, in the present state of human skill and knowledge, is unavoidably and necessarily dangerous to the user is fraught with difficulty. A major portion of the law in this area revolves around cases of hepatitis resulting from blood transfusions. The crucial problem encountered is the nondetectibility of the hepatitis virus in the blood donor. Even though no specific viral detection test has been perfected which can be applied practically to blood banking or plasma pooling, recent observations hold promise for a more accurate method of detecting the asymptomatic carrier of the virus. The impact of this new development cannot be adequately contemplated without an examination of the legal framework in which it must operate.