Two years ago, the author, who has been studying the gorilla Koko and teaching her sign language since 1972, published Koko's Kitten, a moving photographic story about Koko's love for her small pet. This is a fuller biography and update on this charming simian. In a simple text (third graders should have no trouble with it), Patterson, now president of the Gorilla Foundation, describes Koko's language development from the most obvious nouns to abstract thought. Each point is illustrated with incidents and ""quotes"" from Koko herself, providing fascinating glimpses of the relation between reality and the verbal concepts used to represent it. Koko and her friend Michael can not only make direct requests but they can lie, tease, try to delay or divert, call names (""Stupid toilet."" ""Stink bad squash gorilla.""), name a pet (""Lipstick"" for an orange kitten), or reflect real sorrow (on the death of her kitten, ""Cry, sad, frown. . .Blind, sleep cat""). Probably as a result of choosing the best photos and the most interesting incidents, there is not always a close relation between the two (it would have been interesting to have more photos of the gorillas signing), but that is a small cavil. Summarizing Koko's typical day (eating, education and play), the book concludes with a plea for funds for the Foundation's goal of a tropical setting more appropriate to the further study of gorillas than their present California trailer. Although some questions are not answered, this is a fascinating account of the capabilities of one of humankind's nearest relatives, with the appeal of both a heart-warming animal story and serious scientific research. Also good for older children with reading problems.