Cover art has long been used as a marketing device for books, particularly with books aimed at young adults (YAs) aged 12 to 18. An examination of some of the teen thrillers published by novelist Lois Duncan since the 1970s yields several discoveries about changes in cover art that come with various editions. Many covers have been resigned to capitalize on the current teenage taste for blood, gore, and nasty stuff even if the cover implies more terror than actually exists in the story. Current covers also sometimes are devoid of people, so that clothes and hairstyles do not become dated quickly. The conventional wisdom of previous decades was to show adolescents on covers to foster personal identification with the characters. Another trend is to populate cover art with girls or couples regardless of content, in view of the fact that more girls purchase books than boys. Differences are compounded even further in overseas editions. Despite the apparent drawing power of book cover art, publishers seem to have done little or no scientific research on it, preferring to rely on impressions rather than data. They also tend to consult first-level buyers, like booksellers, librarians, and teachers, rather than the teenagers themselves. It is suggested that unknown factors may change too quickly to make research viable, and that adolescents might well be unwilling to open up about their tastes even if they were asked. (BEW)