Measurement of DNA antibodies

Modifications of the standard Farr technic for assaying DNA antibodies are presented; these result in improved separation of normals from abnormals, enhanced reproducibility, and simplicity of performance. The use of 0.4 M borate buffer extends the range of the assay, while a 0.1 M buffer aids differentiation when equivocal results are obtained. Centrifugation of vials prior to counting improves the reproducibility by approximately 3%. Polyethylene glycol, at a final concentration of 6 Gm. per 100 ml., can be substituted for ammonium sulfate, with some advantages.