SUMMARY Tingay, S. 1974. Antiphonal song of the Magpie Lark. Emu 74: 11–17. This paper gives initial results of a field-study of Magpie Larks to investigate the function of antiphonal song. The occurrence of antiphonal calling varies during the year, reaching a peak before breeding and a minimum during care of the young. Antiphonal calls are given more often when the pair is together than apart, especially from roosting and other trees and during joint territorial aggression. During breeding, more circumstances must be classified as ‘apart’ than at other times because one bird is on the nest, but the pair is still often in visual contact while calling. Each pair has a number of varieties of antiphonal call that are used at different times of day. A pair's antiphonal songs carry information about the sexual and individual identity of the caller, probably only for that pair. The primary function of antiphonal song is probably to keep the pair together and to enable co-operation. Its second function is in advertising to conspecifics that the territory is occupied. Only a pair's signature call seems to be given in a different situation from other antiphonal calls and may be particularly important in keeping the birds together.