This is a comprehensive review of all research the authors have conducted into the effects of MDMA on humans, including studies of the subjective effects, their neurobiological correlates, brain activity after MDMA, and changes in pre-pulse inhibition. (Pre-pulse inhibition is treated in this paper as an assessment of information processing.) Knowledge of the pharmacological actions of MDMA reported in in-vitro and non-human animal studies is used as background in discussing the results of human studies, and as a basis for future directions in human MDMA research. The paper also describes the population sampled from in the studies (mostly university students in Zurich) and the standard procedures used in all human MDMA studies conducted by this team. Most information presented in this paper has appeared in previous publications authored by this team (e.g. Gamma et al. 2000; Liechti, et al. 2000a; Liechti et al. 2000b; Liechti et al. 2001; Liechti and Vollenweider 2000a; Liechti and Vollenweider 2000b; Vollenweider et al. 1999, 1998). However, this information is considered in the context of models of psychoactive drug effects, with a focus on suggesting new directions for human MDMA research. This paper does not summarize or address findings from a study assessing the effects of MDMA on an EEG measure of region-specific changes in brain activity (Frei et al. 2001). A discussion of findings from a previously published PET imaging study of the acute effects of MDMA on brain activity are examined in greater detail than in the original publication, with references to research and models of brain activity associated with social cognition or behavior. It is proposed that changes in regional glucose metabolism in the amygdala and temporal lobe may reflect changes in the "basolateral circuit," a circuit or "loop" of areas in the brain found to be associated with social communication. A number of suggestions are made for further research into the neurochemical correlates of MDMA and the relationship between the serotonin system, the dopamine system, and pre-pulse inhibition in humans and rodents.