The marking of sparid otoliths by means of oxytetracycline and alizarin complexone was 'investigated by immersion, feeding and intraperitoneal and intramuscular injections. Of these techniques, immersion for 24 h in a 100-150 mg .1-seawater solution of alizarin complexone was found to be most suitable for marking larval and small juvenile fish. Intramuscular injections of oxytetracycline at a dosage of 250 mg' kg fish-I was the most suitable method for marking the otoliths of juveniles in the laboratory, while dosages between 50 and 100 mg . kg fish-I were used to mark adults in the field. Feeding labelled food to the fish and intraperitoneal injections did not produce a clear mark in the otolith. Auorochrome marks confirmed the daily periodicity of micro-increment formation in some captive sparid species (Diplodus sargus and D. cervinus), and field experiments using Chrysoblephus laticeps showed that this method was a relatively simple way of directly validating age estimates in sparid fish.