This study examined the effectiveness of treating ticks (Ornithodoros capensis) infesting nests of Eastern Brown Pelicans (Pelecanus occidentalis carolinensis). The number of immature ticks on nestling pelicans was significantly less in treated than in control nests. Nest abandonment also was less in treated nests; however, in severely infested nests, treatments did not prevent abandonment. Nesting success and hematocrit measurements did not differ significantly between control and treated groups.