Syrinx is a newly developed PC-based software package designed for interactive playback of animal vocalizations and for digital sound recording and analysis in the lab or in the field. Syrinx permits flexible modeling of complex vocal interactions in an interactive playback setting. Large numbers of sounds can be stored on disk as digital wave files for instant recall in the field. The playback trial timer and real-time scrolling spectrographic display of microphone input facilitate the tailoring of playback responses to subtle changes in the vocalizations of playback subjects. Based on our field test of this software in an interactive playback experiment with Black- capped Chickadees Poecile atricapillus, we conclude that Syrinx is a versatile and user-friendly tool for performing interactive playback with a minimum of equipment.