Ask and you shall receive. Video from NewScientist.
Using two tool-use scenarios (a stick tool-use and a straw tool-use), both chimpanzees were placed in adjacent booths with non-corresponding tools. The chimpanzee in a stick tool-use scenario was given a straw while the chimpanzee in a straw tool-use was given a stick. Successful use of tool resulted in a reward, a carton of juice. A spontaneous tool transfer was observed between paired chimpanzees, mostly following the request of the recipient. Even though reciprocity was not always observed, the chimpanzees continue to assist their partners as long as their partner requested help.
The authors argues that these results further prove the evidence for altruistic behavior in chimpanzees without direct personal gain or immediate reciprocation. These results also highlight the importance of "request" as a cause for prosocial behavior in chimpanzees, between kins or non-kins and also interaction between dominant and non-dominant individuals.
When compared to humans, chimpanzees do not perform acts of voluntary altruism. Unlike humans, chimpanzees do not necessarily act altruistically by just observing another chimpanzee struggle to achieve its goal. Chimpanzees cannot accurately understand others' desires in the absence of communicative signals such as a request.
Further reading on NewScientist.
Yamamoto, S. Humle, T. Masayuki, T. 2009. Chimpanzees Help Each Other upon Request. PLoS ONE 4(10): e7416. [doi:10.1371/journal.pone.0007416]