Gc globulin, also called vitamin D-binding protein, is a plasma protein involved in the actin-scavenger system. In this study, the total Gc globulin concentration in serum or plasma samples was determined using a new, fast, solid-phase inhibition assay. Included in the study were 228 healthy volunteers (131 M, 97 F), 22 pregnant women, 90 cancer patients and 9 patients with chronic liver disease. Moreover, the degree of complexing with actin was determined in selected samples using crossed immunoelectrophoresis. The Gc globulin level in healthy controls was in the range 176-623 mg/L, showing no age dependency. The median level was found to be significantly higher in women than in men. Gc globulin concentrations were raised during pregnancy, showing a median value of 541 mg/L in the first trimester, and slightly raised to 574 mg/L in the second trimester. Cancer patients showed no changes in Gc globulin level, and there was no sign of increased amounts of complexing with actin. Chronic liver patients showed increased levels of Gc globulin following transplantation, but no signs of complexing with actin. This new solid-phase inhibition assay is fast, it is a good complement to the existing quantification methods, and it is especially suitable for determination of the Gc globulin status in acute liver patients before and during treatment.