Background. The possibility that monoaminergic neurotransmission is altered in pathological gambling was examined.Methods. Monoamines and their metabolites were measured in CSF obtained at level L4–5 from ten pathological gamblers and seven controls.Results. A decrease in dopamine and an increase in 3,4-dihydroxyphenylacetic acid and homovanilic acid was found. Noradrenaline and its metabolite 3-methoxy-4-hydroxyphenylglycol was also increased but 5-hydroxytryptamine and 5-hydroxyindoleacetic acid were unchanged.Conclusion. It is suggested that the function of the dopaminergic system, possibly mediating positive and negative reward, and the noradrenergic system, possibly mediating selective attention, is changed in pathological gambling.