Indirect immunofluorescent techniques were used to diagnose active herpes simplex virus ocular infections in 84 patient observations (41 with ocular lesions suspicious clinically for herpes simplex and 43 with lesions suspicious clinically for other ocular inflammatory conditions). We found indirect immunofluorescent antibody techniques to have a high sensitivity (97%) and specificity (73%) when compared to herpes simplex virus cultures. Similarly, we found the sensitivity (98%) and specificity (77%) of indirect immunofluorescent antibody techniques to be high when compared to the clinical diagnosis of herpes simplex viral infection. Significantly, there were no false negative tests by indirect immunofluorescent techniques. Both corneal and upper tarsal scrapings by indirect immunofluorescence were used and the upper tarsal scrapings were an excellent source of cells exhibiting herpes simplex virus antigens. All cases in which corneal scrapings were positive by indirect immunofluorescence for herpes simplex ere also positive by upper tarsal scrapings, although the converse was not true.