A series of three studies investigated the role of play materials in supporting social interactions of nursery school children. Subjects were 14 boys and 11 girls, 4 and 5 years of age, who came from a variety of socioeconomic and racial backgrounds. Observations were made for 16 days, during the free play hour at each of four play centers: art, games, blocks, and dramatic play. The first observational study indicated that, for 4- and 5-year-old children (1) assertive-disruptive interactions occurred most frequently in block play center and least frequently in the art; (2) boys were more often involved in assertive-disruptive interactions than were girls. A second observational study confirmed these results for 4- and 5-year-old children, but not for 1- and 2-year-olds who were also observed. In the third study, available play materials were experimentally manipulated for groups of boys and groups of girls. The behavior of the girls was as expected. The boys, however, showed more assertive-disruptive behavior in art than in blocks. This result is interpreted as supporting the view that the effect of play setting on social interaction is not intrinsic to the play materials but depends upon the child's expectations and knowledge of the situation. (Author/MS)