Abuse of volatile organic solvents among youth remains a major social problem. Organic solvents are cheap and relatively easy to obtain, so they carry the risk of becoming a so-called "gateway drug" for users. Most research regarding organic solvents has until now focused on their neurotoxicity, specifically examining the mechanism of neuron death in terms of the involvement of substances such as nerve growth factor. However, systems to assess psychological dependence on volatile organic solvents that take into account the mechanism involved in the development of this dependence have not been established due to the difficulty of creating animal models. The conditioned place preference procedure, which can easily assess whether psychological dependence has been formed, has been phased in in recent years, and dependence assessment systems have been established for drug inhalation. There have also been new research developments regarding dependence on volatile organic solvents. The importance of mesolimbic dopamine neurons has been indicated in the expression of CNS stimulant action and the development of psychological dependence on drugs such as stimulants, cocaine, and heroin, which are typical abused drugs. It has recently become apparent that the increase in dopamine release in the nucleus accumbens accompanying activation of mesolimbic dopamine neurons, as has conventionally been proposed, is important to the expression of CNS stimulant action and the formation of psychological dependence in response to inhalation of toluene, a volatile organic solvent. Furthermore, research with regard to organic solvents' site of action is also proceeding based on studies using molecular biological techniques. Research regarding toluene is progressing, and the importance of receptors that gate ion channels such as N-methyl-D-aspartate (NMDA) and y-aminobutyric acid (GABA)A receptors as candidates for toluene's site of action has been indicated. Clarification of organic solvents' mechanism for the development of psychological dependence is expected to progress, thanks to analysis focusing on such new sites of action.