This study examined the proposition that Caucasian children between 3 and 5 1/2 years who behave in most sex appropriate ways have a greater knowledge of sex stereotypes than children who do not exhibit such behavior. The children in the study were 35 Most Masuline boys, 31 Least Masculine boys, 38 Most Feminine girls and 39 Least Feminine girls. Forty preschool teachers selected the subjects from 22 classes in 8 private nursery schools in a large metropolitan area by the method of pair comparisons; subjects were then rank ordered. Knowledge of sex stereotypes was measured using (1) a set of 8 pictorial cards depicting stick figures differing on one stereotype feature, and (2) a set of 16 questions concerning sex stereotypes. Individual children were shown the pictorial cards in fixed order and asked to point to the girl or boy. They were then asked 16 questions. Results did not support the hypothesis that knowledge of sex stereotypes and cognitive maturity affect sex role behavior. Girls were found to have more knowledge of sex stereotypes in general as well as of their own sex stereotypes when compared to boys. It is proposed that more attention be paid to the establishment of criterion groups in studies attempting to explore the process of sex role development which is still little understood. (GO)