The cytoplasmic membranes of cells infected with herpes simplex virus develop altered antigenic specificities (O'Dea & Dineen, 1957; Roizman & Spring, 1967). Strain-specific differences in these surface antigens have been reported (Roizman & Roane, 1963; Peterknecht, Bitter-Suerman & Falke, 1968). In the course of a study of antigenic specificities in BHK cells infected with several herpes simplex viruses (cf. Watson et al. 1966), we have found that the use of appropriately absorbed antisera permits the detection of type-specific membrane antigens. This forms the basis of the simple and rapid immunofluorescent method for typing strains of herpes simplex virus which we report in this note. Exploratory work was done with two established type 1 strains (hfem which originated from the Rockefeller strain hf and wal, a recurrent oral isolate) and two established type 2 strains (lov, kindly given us by Dr A. J. Nahmias and bry, a recurrent genital isolate).