Ciproxifan belongs to a novel chemical series of histamine H3-receptor antagonists. In vitro, it behaved as a competitive antagonist at the H3 autoreceptor controlling 3H histamine release from synaptosomes and displayed similar Ki values (0.5-1.9 nM) at the H3 receptor controlling the electrically-induced contraction of guinea pig ileum or at the brain H3 receptor labeled with 125I-iodoproxyfan. Ciproxifan appears to be an orally bioavailable, extremely potent and selective H3-receptor antagonist whose vigilance- and attention-promoting effects are promising for therapeutic applications in aging disorders.