In large scale commercial pig production the programmed replacement of culled sows by pregnant gilts is a major problem. Techniques for heat synchronisation in groups of gilts have been explored by a number of workers using a variety of materals such as methallibure, gonadotrophins and progesterone. One promising method involves the use of allyl-trenbolone as an agent for oestrous synchronisation (Varley, 1983; Stevenson and Davis, 1981). Another approach is to use a combination of gonadotrophins (PMSG and HCG) to induce ovulation and new oestrous cycles.The purpose of this study was to compare the value of these two techniaues under the same commercial conditions.