We propose that homozygosity for the Bal I polymorphism DRD3 gene is associated with predisposition to substance abuse and/or the pharmacosensitive characteristic of schizophrenia rather than with schizophrenia itself, an hypothesis in agreement with the positive association of this polymorphism with opiate dependence (see companion article by Duaux et al) and the involvement of DRD3 in both pharmacodependence mechanisms and antipsychotic effects of neuroleptics.