The temporal lobe in the left hemisphere has long been implicated in the perception of speech sounds. Little is known, however, regarding the specific function of different temporal regions in the analysis of the speech signal. Here we show that an area extending along the left middle and anterior superior temporal sulcus (STS) is activated more extensively by familiar CV syllables during an auditory discrimination task, than by comparably complex auditory patterns which cannot be associated with English learned phonemic categories. In contrast, areas in the dorsal superior temporal gyrus bilaterally, closer to primary auditory cortex, are activated to the same extent by the phonemic and non-phonemic sounds. Thus, the left middle/anterior STS appears to play a specific role in phonemic perception. It may represent an intermediate stage of processing in a functional pathway linking areas in bilateral dorsal STG presumably involved in the analysis of physical features of speech and other complex non-speech sounds, to areas in the left anterior STS that are engaged in higher-level linguistic processes.