This exploratory study investigated whether the Brazelton Neonatal Behavioral Assessment Scale (NBAS) can predict an infant's behavior on mastery motivation tasks at 1 and 2 years of age. Subjects were 31 normal, full-term infants from white, mostly middle class families. Infants were assessed using the NBAS with Kansas Supplements (NBAS-K) at a mean age of 11.93 days. Seventeen of these infants participated in a mastery task session at a mean age of 24 months 23 days. When NBAS-K scores were correlated with later mastery scores, neonates judged to be difficult and willful were found to be more persistent, more competent, and to express relatively more task pleasure and less negative affect on the mastery tasks. These results are similar to studies that have shown socially valued neonatal behavior (e.g. alertness and consolability) to be negatively related to equally valued later behavior (e.g. competence). (MM)