Teachers and mothers of 219 four-year-old preschoolers assessed their children for Type A behavior pattern using the Matthews Youth Test for Health (MYTH). The sample was derived from five day care centers with Black, White, and Hispanic teachers and students from middle and lower class families. This study indicates that Type A behavior can be identified in four-year-old preschoolers on the basis of ratings by their teachers. A statistically significant difference was found between the ratings of Type A/B characteristics by teachers and those by mothers; however, these were not related to the sex or ethnicity of the children. Repeated measurements of Type A ratings in a subsample of the children at age five showed no significant change among boys or girls. However, repeated measurements at age six on a second subsample showed that boys had lower mean scores, i.e. were more Type B at age six than at age four.