Patch tests with 15 different 8-hydroxyquinolines and with quinoline were performed on 9 patients primarily sensitized to 5,7-dichloro-8-hydroxyquinoline. Besides sensitivity to 5,7-dichloro-8-hydroxyquinoline there was a strong effect against 7-chloro-8-hydroxyquinoline, less against 5-chloro-8-hydroxyquinoline and the mildest sensitization activity to 8-hydroxyquinoline. Regarding the methyl-8-hydroxyquinolines only the 7-methyl compound gave positive reactions whereas 5- and 2-methyl-8-hydroxyquinoline were without effect. The sensitizing ability was abolished by blocking of the 8-hydroxyl group or by oxidation of the N-atom of quinoline to N-oxide.