A study was conducted to create an instrument for systematically coding qualitative processes of children's cooperative and associative play. Data were gathered through observations of 16 preschool children ranging in age from 47 to 59 months and attending a day care center using the High/Scope Preschool Curriculum Model. A total of 20 hours of children's dialogues were recorded verbatim and a partial record of children's behavior was videotaped. Transcribed data were entered into a word processor in transcription format. Transcripts were cut into series of exchanges and affixed to index cards. Appropriate contextual notes were made on the cards. Exchanges on cards were then sorted according to similarities and recurring behaviors. The categories used in the coding system emerged from the sorting process. Guiding questions were used as references for establishing the parameters of each category. The 11 preliminary categories of social play which emerged from the sorting process were analytically reduced to 8. These categories included entering and establishing behaviors, ownership and object exchange, assistance seeking and providing, directing behaviors, declaring and extending behaviors, denying or offering friendship, comparison and display, and exiting and closing behaviors. Directions for further research are offered. (RH)