Wild chimpanzees ( Pan troglodytes) produce low-frequency sounds by hitting the buttresses and/or trunks of trees. This "buttress drumming" occurs in discrete bouts that may be integrated into the phrase sequence of the chimpanzee's long-distance vocalization, the "pant hoot." The aim of this study was to investigate whether regional variation exists in the drumming behavior of male chimpanzees from Kibale National Park (Kanyawara community), Uganda, and Taï National Park, Ivory Coast. Recordings were made during a 6-month field season at Taï in 1990, and a 12-month field season at Kanyawara in 1996-1997. Acoustic analysis revealed the following: (1) Kanyawara males drummed significantly less frequently in conjunction with a pant hoot or hoot than did Taï males; (2) drumming bouts by Kanyawara males included significantly fewer beats, and were significantly shorter in duration, than those of Taï males; these differences disappeared when only those bouts produced in conjunction with a call were compared; (3) when Kanyawara chimpanzees did call and drum together, they tended to integrate drumming into the vocalization at a later point than did Taï males; and (4) individual differences in the temporal patterning of drumming bouts were not apparent for Kanyawara males, whereas a previous analysis revealed individual differences among Taï males.