Soluble fibrin monomer complexes were assayed by agarose gel filtration and by ultracentrifugation. Increased values of SFMC were found in the normal third-trimester pregnancies. They were considerably higher in plasma of patients with pre-eclampsia. Concentrations were higher using ultracentrifugation as compared to gel chromatography. Using ultracentrifugation 4 components were identified, indicating that SFMC in this disease are not a homogeneous group.