Discusses complex trait-treatment-interaction (CTTI) analysis, a new statistical method for studying the combined effects of personality traits and treatments on some particular aspect of human behavior. The method involves the initial study of trait interactions within experimental groups by plotting regression surfaces. A linear model containing higher-order interactions is then specified and tested using a standard ordinary least-squares algorithm. Application of CTTI analysis is demonstrated using data acquired in a previous study concerning the effects of catecholamine synthesis inhibition on alcohol-induced changes in psychomotor performance. 80 healthy male subjects (aged 20-35 years) were examined regarding two personality traits: anxiety (State-Trait Anxiety Inventory, STAI) and impulsiveness (Extraversion Scale of Eysenck Personality Inventory, EPI). The results of CTTI analysis supported the hypothesis that the correlation between one or more trait variables and performance variables (human behavior) is moderated by one or more treatments. The statistical power of CTTI analysis is discussed and compared to that of other statistical approaches to complex trait-treatment-interaction analysis.