To investigate if antiparasitic treatment of reindeer calves during the summer could increase their carcass weight during the slaughter period in autumn and winter, 529 reindeer calves were allocated to three groups, weighed, and marked with individually numbered plastic ear tags in early July, 1995. One of the groups was left untreated, another was treated with ivermectin injection at 200 micrograms/kg, and the third with pour-on ivermectin at 500 micrograms/kg. Following slaughter, carcass weights were received from 231 animals, and there was no difference between the treatment groups.