A total of 253 cows was treated using 500mug cloprostenol intramuscularly. Of those, 129 cows were treated for failure to exhibit an observed oestrus, 124 for being negative at pregnancy diagnosis examination; all possessed a corpus luteum as detected by rectal palpation. One hundred and sixty nine (66.8 per cent) were detected in oestrus within eight days, and of these 159 were served. Eight-seven (54.7 per cent) of them conceived. Sixteen cases of luteinised ovarian cysts were also treated with a resultant 14 conceptions occurring at a mean interval of 19-4 days. It is condisered that the time of the induced oestrus is not predictable enough to warrant "fixed time" insemination. The success of treatment will be related to: (1) The efficiency of oestrus detection on the farm (2) The normal conception rate on the farm (3) The accuracy of the rectal palpations.