Technical Abstract: The effectiveness of a pour-on formulation of novaluron (Novatack Pour-on 5% AI), a benzoylphenyl urea acaricide, was evaluated by applying low and high rates (1 mg/20 kg body weight and 1 mg/10 kg body weight) to cattle infested with all parasitic developmental stages (adults, nymphs, and larvae) of Rhipicephalus (Boophilus) microplus (Canestrini). The therapeutic percentage reduction in the number of females that reached repletion following treatment was 24.8 and 24.6% for the low and high rates, respectively. No difference in the weight of engorged females recovered from treated calves or in the index of fecundity (IF) was observed for either rate in comparison with the untreated control, and no significant difference in the overall therapeutic level of control was observed between the low and the high rates. Results obtained from the analysis of persistent (residual) efficacy of both rates showed no significant differences between the treatments at weekly intervals. However the percent control of the IF observed against larvae infested one and two weeks after treatment for both rates is moderate indicating that novaluron appears to be more effective against larvae that come into contact with cattle after treatment than against adults or nymphs already infesting the animal at the time of treatment. The potential for use of the tested rates of pour-on novaluron in the USDA-APHIS- Cattle Fever Tick Eradication Program is discussed.