In order to assess whether response to the natural precursor of catecholamines in the nervous system is impaired in atopy, 500 mg L-dopa was administered to 13 atopic patients with bronchial asthma or hay fever and 13 sex-and-age-matched control subjects. The blood eosinophil count and growth hormone (GH) levels were then determined periodically over a 4-h period. The eosinophil count rose significantly 30 and 60 min after L-dopa in healthy subjects, but not in the atopic patients. The mean rise in GH 30 and 60 min after L-dopa was significantly lower in atopic patients as compared with controls. Injection of apomorphine 0.75 mg elicited increase in GH in nine of the 10 control subjects, but only in six of the 11 atopic patients. These results indicate that central dopaminergic stimulation is often impaired in patients with atopy. In testing GH release, atopy should be considered among the causes of failure to respond.