Child psychoanalysts have long viewed play as a reflection of children's inner lives and have used the themes children represent in play for diagnostic and therapeutic work. Given the central role children's play has for clinical work, few studies have addressed play empirically. This paper presents a technique for studying the thematic content of children's play as it emerges during a play session with a child analyst. We report the steps involved in developing this investigative technique and describe the interobserver agreement among four raters using the technique with videotaped play sessions. Implications for future research using such an approach are discussed.