The serum haptoglobin concentration was measured by rate nephalometry in 56 patients with invasive carcinoma of the cervix, and in 24 women with no evidence of cervical pathology who served as control subjects. There was a significant difference in the mean serum haptoglobin concentration (p less than 0.005) between the 2 groups of patients. However there was no significant correlation between the serum haptoglobin concentration and the clinical stage of the disease. From our data we propose that a serum haptoglobin concentration greater than 96 mg/dl is suggestive of invasive carcinoma of the cervix, and that this may be used as additional investigation in the initial assessment of such patients.