Addiction is a condition where organism feels a strong psychological or physical need for narcotic substance. Psychostimulative drugs, like cocaine and methamphetamine, affect neural mechanisms involved in the processing of rewards. Because of the rewarding effect of a drug, attraction for a drug leads to addictive behavior. This behavior can be investigated in laboratory animals as preferential consumption. Although there are many assays to measure locomotor effects of cocaine and methamphetamine, a way to measure rewarding influence of psychostimulants in Drosophila melanogaster has not yet been developed. The aim of this thesis was to define the characteristics of preferential consumption for cocaine and methamphetamine in fruit flies as a model organism to study addictive behaviors. In order to do that, we modified the Capillary Feeding (CAFE) essay initially designed to test alcohol dependence. We find that fruit flies willingly self-administrate cocaine and methamphetamine and develop patterns of addictive behavior similar to ones observed in humans and rodent models. Fruit flies actively choose and prefer food with cocaine or methamphetamine despite of bitter taste of these psychostimulants, they continue to consume drugs despite negative consequences and after deprivation develop behaviors similar to relapse. Our results suggest that the development of preferential consumption for cocaine depends on cycle gene products, that preference for methamphetamine involves period, Clock and cycle genes, and that dopamine transporter and dopamine receptor type 1 are not involved in the development of preferential consumption. The use of Drosophila in self-administration experiments will be useful in further research on neurological mechanisms of rewarding action of psychostimulants, with final goal of designing pharmacological treatments for prevention and treatment of addiction.