|Abstract||Fine wool Merino sheep with short (4 mm) or long (30-80 mm) wool and moderate to heavy infestations of lice (Bovicola ovis) were treated with cyhalothrin at a concentration of 50 mg/L, applied using Alison, Aussie Dip and Boral Cyclone Superace automatic jetting races. Each machine was set up and operated by representatives of the manufacturer. With all 3 machines, arithmetic mean louse counts before and after treatment showed that in the sheep with short wool, lice numbers were reduced by greater than or equal to 98% at 8-12 weeks after treatment but were not eliminated. In the sheep with long wool, the maximum reductions in mean louse counts were 79, 68 and 98% for Alison, Aussie Dip and Boral Cyclone Superace machines at 7, 5 and 8 weeks after treatment, respectively. The Alison and Aussie Dip machines were each tested in alternative configurations which affected the disposition of the jetting fluid on the fleece. The distribution of live lice on the bodies of the shorn sheep after treatment using the Alison machine and 1 configuration of the Aussie Dip machine, indicated that more insecticide may have been delivered to the left side of the body than to the right. There were no significant differences between sides in sheep treated in the Boral Cyclone Superace machine. Our results suggest that the jetting races tested would control infestations of lice for at least 12 weeks in sheep treated within 2 weeks after shearing, but would be unlikely to eradicate lice from an infested flock. The machines differed markedly in their ability to control moderate to heavy infestations of lice in sheep with long (30-80 mm) wool, but in all cases there was evidence of a resurgence in lice numbers beyond 12 weeks after treatment.