A multimethod, multitrait approach was used to examine the relations of aggression and hyperactivity to mastery motivation in preschool children. Parallel measures of multiple facets of mastery motivation were devised from findings in two studies: (study 1) a maternal report questionnaire for 332 twins, ages 3-5, recruited from the twin registry in a Western state; and (study 2) behavioral observations and ratings by trained preschool personnel from the Bethesda Longitudinal Study for 152 normally developing, middle to upper income children during their first 3 years. The findings from both studies indicated that high involvement in and/or vigor at gross motor tasks was associated with high activity, impulsivity, and aggression in preschoolers. Persistence at challenging object-oriented tasks contributed negatively to predicting hyperactivity (Study 1) and impulsivity (Study 2), but did not predict activity level (Study 2), suggesting that the impulsivity aspect of hyperactivity is what is negatively associated with low task persistence. It is argued that, given the high incidence of attention deficit disorders with hyperactivity (ADHD) and aggression in school settings, it is important to study their precursors in preschoolers. Data from the two studies imply that it is important to distinguish between high activity level and hyperactivity, which includes elements of impulsivity and difficulty in maintaining attention to tasks. Teachers may misinterpret social or gross motor mastery attempts, accompanied by high activity level, as ADHD so should be cautioned not to overinterpret what they see. (Contains 11 references.) (KB)