A total of 103 preschool children of lower and middle socioeconomic status families were observed in three preschool programs during 15 standardized free play periods for the purpose of investigating preschool children's preferences for different types of traditionally used play materials. The influence of age, sex, and socioeconomic status (SES) on the children's preferences was also examined. Children of different racial and ethnic backgrounds were integrated into all groups. Seven categories of materials were defined and materials for each category were made available to the children each day of observation; materials included art materials, role play materials, blocks, sand, playdough, manipulatives, and wheeled vehicles. Teachers were asked to assume a supervisory, but nonparticipatory, role. A time sampling technique was used to gather the data. Findings indicated: (1) a preference for some kinds of structured materials over unstructured materials; (2) sex differences in preferences; (3) the preference of lower SES children for sand, playdough, wheeled vehicles, and role play materials; and (4) the preference of middle SES children for art materials and blocks. Overall, role play materials were used significantly more than any other material. Implications for early childhood education and for further research are pointed out. (RH)