The interaction between standard heparin, low-molecular-weight heparin (LMWH), and granulocyte-colony stimulating factor (G-CSF) was studied by capillary zone electrophoresis. Both qualitative and quantitative characterizations of the heparin-protein binding were determined. The binding constants of the two different groups of heparins with G-CSF, calculated from the Scatchard plot by regression, were 4.805 x 10(5) M(-1) and 4.579 x 10(5) M(-1), respectively. The two binding constants measured are of the same order of magnitude at 10(5) M(-1), indicating that LMWH contains most of the functional groups bound to G-CSF by standard heparin.