A microelectrophoresis procedure on agarose for heparin and related compounds and a simple electrophoretic chamber are described. The method permits simultaneous identification and measurement. Identification is made by migration of the sample relative to that of reference heparin. International Heparin Standard, a number of commercial heparins, and whale and dog heparin have 2 components on microelectrophoresis. Leo heparin contained only 1 component and was used as the reference material. Migration rates relative to Leo heparin were: hyaluronic acid, 0.70; chondroitin sulfate A/C, 0.87; chondroitin sulfate B, 0.866; heparinoid-G31150, 0.94; dextran sulfate, 1.06; International Standard heparin, 0.89-1.01; commercial heparins, 0.89-1.01; dog heparin, 0.90; whale heparin, 0.85. For quantitation, heparin is applied to the slide by micropipette and the optical density of the stained spot measured by densltometer. This is converted to international units from the curve obtained for optical density with varying amounts of International Heparin Standard. Microelectrophoretic equivalents (expressed in terms of international heparin units) were for Leo heparin, 0.99 units = 1.00 international unit; for commercial heparins, values were between 84 and 134 international units/mg. Heparin after injection can be demonstrated by this method in perfusion fluid tissue, blood, and urine.