Significant progress in the development of potent and selective histamine H1-receptor agonists has been achieved since 1990. Optimisation of the class of 2-phenylhistamines has furnished 2-[3-(trifluoromethyl)phenyl]histamine and its Nalpha-methyl derivative. The discovery of histaprodifen (2-[2-(3,3-diphenylpropyl)-1H-imidazol-4-yl]ethanamine) and the novel lead compound suprahistaprodifen (Nalpha-2-[(1H-imidazol-4-yl)ethyl]histaprodifen) represents additional milestones in the H1-receptor agonist field.