Interaction of various ligands with recombinant proteins of 5 human FABP types was studied by radiochemical and fluorescence procedures. Liver, heart, intestinal and myelin FABP showed a higher affinity for oleic acid than adipocyte FABP. Intestinal and adipocyte FABP had a relatively high Kd value for arachidonic acid. Liver and intestinal FABP showed high affinity for DAUDA in contrast to the other FABP types. ANS was only well bound by liver and adipocyte FABP. Retinol was not bound by any FABP type, retinoic acid only by adipocyte FABP. Data indicate the importance of both electrostatic and hydrophobic interaction for the ligand-FABP binding. The immunological crossreactivity between six human FABP types including epidermal FABP and their respective antibodies raised in rabbit, chicken and mouse appeared to be low and may suggest heterogeneity of protein surface.