Fifty Bos taurus x Bos indicus heifers naturally infested with Boophilus microplus ticks were divided into two groups of 25 heifers each. Individuals of one group were treated with moxidectin 0.5% pour-on at a dosage of 500 microg of moxidectin/kg body weight and heifers from the other group remained as untreated controls. An efficacy higher than 95% was found on days 7-21 after treatment by using female ticks 4.5-8.0 mm long as the main infestation parameter. A lower, but significant efficacy (p < 0.05) was also found on days 1 (32.3% efficacy) and 27 (73.4% efficacy) post-treatment. Significantly (p < 0.05) lower numbers of immature ticks were also observed on heifers of the treated group from days 7 through 27 after treatment. A lower engorgement weight of female ticks from treated heifers was found on days 1 and 21 after treatment. Treatment also affected reproductive performance (oviposition, egg hatch and number of eggs laid) of female ticks collected on Day 1.