Psychological hedonism is the theory that all human choice is motivated by a desire for pleasure (or an aversion to suffering).
This theory of human motivation cannot rule out altruism without being contradicted by evidence. Rather, it claims that when sane people choose to help others, it is because of the pleasure they themselves obtain, directly or indirectly, from doing so. Psychological hedonism is a special case of psychological egoism, in which the concept of "self interest" is equated with pleasure.
All the arguments and counter-arguments presented in the article on psychological egoism also apply to psychological hedonism.
See also: Hedonism