Two regions of the human prodynorphin gene, the exon 4-region coding for the opioid peptides and the putative promotor/exon 1-region were analyzed for possible presence of polymorphisms. No polymorphism was detected in the exon 4-region, whereas a GC/AT base-pair exchange was observed 301 base pairs upstream of the exon 1/intron A boundary. This polymorphic marker was examined in Scandinavian chronic alcoholics (n = 70) and control subjects (n = 55). Prodynorphin allelic distributions were not significantly different in alcoholic patients and control subjects. The results suggest that no major influence on alcoholism is exerted through genes associated with this prodynorphin allelic marker.