In this study, 24 adult patients with head lice will be treated with a topical malathion head lice treatment; 12 patients will be treated with a novel product, Malathion Gel, 0.5%, and other 12 patients will be treated with Ovide Lotion 0.5% marketed by Taro Pharmaceuticals USA, Inc. The primary objective of this study is to compare the blood level exposure of Malathion 0.5% Gel to that of the OVIDE Lotion 0.5%.