The ability to detect oestrus in cattle is important where artificial insemination, superovulation or embryo transfer techniques are being used. Even where oestrus is synchronised or controlled, knowlege of the occurrence of oestrus can increase success rates and reduce costs. A testosterone treated female fitted with a chinball marker (Signoret, 1975; Kiser, Britt and Ritchie, 1977) has been shown to be a useful aid to detection of oestrus. A preliminary experience using such females in conjunction with maiden heifers supported these claims and a subsequent trial provided a more formal evaluation of the technique.