This study was designed to evaluate, in healthy volunteers, differences of bronchodilator responsiveness to a beta 2-agonist between those with the Arg 16/Gly 16 allele and those with the Gly 16/Gly 16 allele at codon 16 of beta 2 adrenoceptor polymorphism. Peak flow and pulmonary functions were measured by body plethysmography after the inhalation of procaterol. In the Arg 16/Gly 16 group, the resulting acute increase of V 25 and acute decrease of airway resistance were greater, and the bronchodilator effect of a single inhaled beta 2-agonist was longer, than those observed in the Gly 16/Gly 16 group. The present study showed that a single inhalation of procaterol has a varying bronchodilator effect on healthy adults, depending on the genotype of beta 2 adrenoceptor polymorphism at codon 16.