Two cases of eczema herpeticum are reported. Because of widespread vesicular eruption, high fever, and severe, prolonged disease both were thought to be primary infections. Laboratory examination found one to be a primary infection and the other recurrent. This emphasizes the necessity for laboratory study in differentiation of these two types of eczema herpeticum. In the infant there was no apparent influence of 77 ml of γ-globulin given in eight day's time on the course of a primary infection despite significant herpes neutralizing titers in the γ-globulin and in the child's serum. Severe and extensive eczema herpeticum developed in an adult despite high neutralizing antibody content of her serum. Although conventional neutralizing antibody probably plays some role in cure or control of herpes simplex infections, other largely unknown mechanisms may be equally important.