To investigate the development of symbolic play, 18 Japanese normal boys and girls were individually tested once every even-numbered month from when they were 12 to 24 months of age. Symbolic play was generally defined as behavior which represents actual or imagined experience by using objects, gesture or language alone or in combination. The symbolic play behavior was further specified in terms of three types of representation (material, gestural, verbal), three types of agent use (self, passive other, active other), and three types of elaborated acts (unordered, combination, and organized multi-scheme combinations). Testing took place in laboratory settings with materials composed of three sets of miniature toys, a doll, and junk materials. Each set was presented for 5 minutes and the subject's spontaneous behavior was videotaped. Additionally, a trained observer took notes when there was difficulty in interpreting the subject's pretend behavior, especially when substitute use of the materials or gestural representation occurred. After each session, the observer asked the mother about these behaviors as well as the subject's pretend use of real objects in everyday life. Seven items of data were selected as measures of the development of symbolic play such as percentage of occurrence of symbolic play, substitute object use, and other agent use; and total number of different acts and different referents in substitute object use. (Author/RH)