During open brain surgery under local anesthesia for the treatment of medically intractable temporal lobe epilepsy we have recorded neuronal activity from the lateral temporal lobe with microelectrodes while the patients listened to short pieces of music. Three groups of music were tested: A) Simple familiar or unknown classical tunes at a simple rhythm and harmony, played on piano; B) Orchestrated folk music; C) Drumming without a tune. All types of music lead to changes of neuronal discharge rate. Musical pieces of type A produced a decrease in 48% of the recordings, an increase in about 17% and had no effect in 30%. A similar distribution of effects was found during type B-music (48%, 22%, 30%, respectively). During type C, only 26% showed a decrease and 74% an increase. When music was turned off, usually the reverse change from that caused by music was seen. In addition to changes of discharge rate, a slight entrainment of activity by single, regularly appearing notes (rhythm) was seen in some neurons. A few neurons showed a change of activity related to musical phrases (activation towards the end of a 4-bar 4/4 phrase). In contrast to the effects of verbal stimuli and overt speech, the effects of music on discharge rates did not show obvious topographical differences between superior, middle and inferior temporal gyrus. They also were bilateral with no significant right-left differences.