Growth hormone (GH) and beta-endorphin (beta-EP) responses to clonidine stimulation were examined in 18 male heroin addicts, 9 with and 9 without previous histories of attention deficit disorder with hyperactivity (ADD-H) and conduct disorder (CD). Ten psychophysically healthy volunteers were used as controls. ADD-H/CD addicts had blunted GH and beta-EP responses as compared to controls while those of non-ADD-H/CD addicts were normal. This suggests that postsynaptic adrenoceptor sensitivity is decreased and, possibly, that presynaptic noradrenaline secretion is increased in ADD-H/CD patients with heroin addiction.