Fifty-seven patients with ocular herpes simplex (HS) infection were studied for evaluation of existing methods for virus isolation and its application in diagnosis of HS infection. Virus was isolated in 90% of 34 cases with keratitis dendritica, when specimens were taken within eight days of onset of symptoms. The same isolation frequency was obtained in 10 cases of palpebral herpes with conjunctivitis. No isolation was possible in 11 cases of keratitis disciformis. Laboratory confirmation was obtained within four days in 70% of the positive cases. Ten strains of HS virus type 1 were examined for IDU resistance, 5 strains isolated prior to and 5 during IDU treatment. Nine of the strains had the same degree of sensitivity. One strain isolated during treatment was found to be highly resistant.