In 1982 Hamilton and Zuk(1) proposed a provocative solution for the unexplained fact that the males of many species exhibit 'showy' traits such as brightly coloured plumage or vigorous courtship displays. They suggested that showy traits are fully expressed only by males who are resistant to parasites and that females examine such traits in order to choose resistant males as mates. Hamilton and Zuk's proposal has been the topic of extensive research and vigorous debate for nearly a decade. This article reviews the research, relevant criticisms and unanswered questions pertaining to the influence of parasites on sexual selection.