Herpes simplex virus (HSV) infected cells have been detected in tissue culture and human cell specimens by an immunoenzymatic staining method using the fungal enzyme glucose oxidase. Infected cells from culture or human specimens appear as dark blue, brown, or red, depending on the tetrazolium salt used in the disclosing reaction, with virtually no staining of uninfected cells. The specificity and sensitivity of this method and of the more commonly used immunoperoxidase method are comparable, but the immunoglucose oxidase method avoids the problems of nonspecific staining by the endogenous peroxidase present in mucosecretions and inflammatory cells. Staining time can be reduced up to 40% of that necessary for the unlabeled immunoperoxidase procedure without compromising the quality of staining results.