Various side effects due to anti-herpetic drugs observed in the last ten years in our department were studied. A total of 132 patients were treated with 5-iodo-2′-deoxyuridine(IDU), 69 with trifluorothymidine(F T), 58 with acyclovir (ACV) and 33 with adenine arabinoside (ara-A). Patch tests were routinely done when patients exhibited contact dermatitis. Of the patients treated with IDU, 3(2.3%) showed contact dermatitis, 2(1.5%) follicular conjunctivitis and 1(0.8%) punctate keratopathy. Of the patients treated with F3T, 7(10. 1%) exhibited contact dermatitis and 1(1.4%) follicular conjunctivitis. In the group treated with ACV, 2(3.4%) patients showed punctate keratopathy. The patients who received ara-A did not show any side effects. We found that FT caused contact dermatitis more frequently in Japanese people than Europeans. These side effects were resolved by switching to another anti-herpetic drug without the occurence of cross-allergy. Therefore, switching to another drug is strongly recommended when patients exhibit side effects in the treatment of herpetic keratitis. Other complications were allergy to atropine and to drug preservative.