Four experiments investigated the perception of tonal structure in polytonal music. The experiments used musical excerpts in which the upper stave of the music suggested a different key than the lower stave. In Experiment 1, listeners rated the goodness of fit of probe tones following an excerpt from Dubois's Circus. Results suggested that listeners were sensitive to two keys, and weighted them according to their perceived importance within the excerpt. Experiment 2 confirmed that music within each stave reliably conveyed key structure on its own. In Experiment 3, listeners rated probe tones following an excerpt from Milhaud's Sonata No. 1 for Piano, in which different keys were conveyed in widely separate pitch registers. Ratings were collected across three octaves. Listeners did not associate each key with a specific register. Rather, ratings for all three octave registers reflected only the key associated with the upper stave. Experiment 4 confirmed that the music within each stave reliably conveyed key structure on its own. It is suggested that when one key predominates in a polytonal context, other keys may not contribute to the overall perceived tonal structure. The influence of long-term knowledge and immediate context on the perception of tonal structure in polytonal music is discussed.