Highly sensitive measurement of cytosolic proteins allows early and rapid detection of loss of cell membrane integrity. Small unbound cytosolic proteins show a rapid release from damaged cells. The detection of cell damage is of importance in cellular toxicology studies and in various experimental and clinical situations. Examples of the latter are myocardial infarction and liver transplantation. Members of the family of Fatty Acid Binding Proteins (FABP) with tissue specificity with a molar mass of approximately 14 kDa have been found to be very useful for this purpose. Ischemically damaged tissues release FABP rapidly enabling early detection of ischemically damaged organs. Further ischemically damaged organs are characterized histologically by (near) absence of FABP facilitating recognition of such areas. Various types of FABP have been discovered: Heart FABP (primarily present in heart and striated muscle cells but also of interest as brain damage marker), Liver FABP (present in liver and proximal small intestine), Intestinal FABP (present in small bowel epithelium), Ileal-FABP (ILBP) and many more. HB has a broad range of antibodies and ELISA assays for various species that allow quantification of a series of FABP.