Cytosolic fatty acid-binding proteins (FABPs) were first described in 1972 and, during several years, most of the studies involved only mammals. These proteins are present in nearly all mammal tissues and a high degree of primary structure similarity has been found between FABPs of the same tissue in different species. They were classified into several types - such as liver, heart, intestinal, adipocyte, myelin, ileal and epidermal - on account of the first tissue they were isolated from. However, this tissue specificity does not hold true for fish. We have reviewed the chief publications on molecular evolution of these proteins and comment herein on the amino acid sequence of over 60 FABPs and those evolutionary trees proposed so far. Our contribution concerning the evolution of the different types is presented in a chronological relation to previous papers by other authors and also to those appearing later on. We have isolated over 15 FABPs from different animals (chimera fish, elasmobranchs, bone fish, amphibians and mammals) and partially or fully determined their primary structure. Our results are discussed in relation to the current hypotheses.