The H1-receptor antagonists (H1-antihistamines) are among the most widely used medications in the world. We review the molecular basis of action, pharmacology, efficacy in allergic disorders (rhinoconjunctivitis, asthma, urticaria, atopic dermatitis) and adverse effects. Special advices are given for the young children, the elderly, in case of liver or renal insufficiency and during pregnancy and breast-feeding.