This experimental study was conducted in the inpatient detoxification addictive behavior unit of the Sant Pau Hospital in Barcelona and included 22 healthy subjects (HS) and 42 intravenous heroin-dependent subjects (HDS). Apomorphine-induced yawning rates were investigated in three different groups; heroin-dependent patients stabilized on d-propoxiphene, heroin-dependent patients recently withdrawn from d-propoxiphene and normal controls. Yawning responses were recorded continuously by independent observers for periods of 45 minutes following administration of low doses of subcutaneous apomorphine and NaCl. The lowest subcutaneous apomorphine dose able to induce a significantly higher number of yawning responses in HS was 0.005 mg/kg. The yawning responses induced by this dose in HDS were also significantly higher than those induced by placebo. When comparing the number of yawning responses between the study groups, differences were observed only between HDS and HS and no effect of gender was obtained. The apomorphine test may be useful in assessing central dopamine system alterations associated with chronic heroin consumption and could be a stable and reliable biological marker of heroin-dependence disorders.