The respiratory tolerance can limit the use of beta-blocker medication (beta-) currently indicated in numerous clinical situations, both cardiovascular and also neurological and ophthalmological. Blockade of beta adrenergic receptors is without risk in subjects free of bronchial pathology, but may destabilize underlying airflow obstruction; either presenting as or sustaining bronchospasm in an asthmatic, and increasing bronchial obstruction, in patients suffering from chronic airflow obstruction (BPCO). Now BPCO, and in particular asthma, are easily associated with diseases for which beta- are indicated. In addition the notion of cardioselectivity is relative and dose dependent. CONCLUSIONS beta- are contraindicated in chronic airflow obstruction with bronchial hyper-reactivity; in other cases, beta- should be used carefully choosing the most cardioselective products at the lowest effective dose. Whatever the route of administration (in particular eye drops), the beta- are reliable to produce the same harmful effects. There should be strict follow up of treatment and a watch kept for signs of a worsening or a provocation of respiratory problems; conversely the occurrence of such symptomatology in a patient with bronchial pathology should call into question the place of beta-. Finally beta- should be avoided in allergic subjects and (a fortiori) in specific immunotherapy where there is a possibility of anaphylactic shock.