The soluble material produced from a 96-hour digest of sonicated human glomerular basement membranes with purified collagenase was shown to contain at least 12 components by sodium dodecyl sulphate-polyacrylamide gel electrophoresis with molecular weights ranging from 20×10<sup>3</sup> to greater than 200 ×10<sup>3</sup> daltons. Five of these components produced antigenic peaks after two-dimensional immunoelectrophoresis into agar plates containing rabbit antiserum to the solubilised glomerular basement membrane. Two groups of antigenic components were demonstrated in these gels by two-dimensional immunoelectrophoresis autoradiographic techniques utilising <sup>125</sup>I-labelled collagenase-digested human glomerular basement membranes reacted with antibodies eluted at acid pH from the kidney of the Goodpasture’s patient. This acid eluate was shown to contain contaminants of α<sub>1</sub>-antitrypsin and albumin co-eluting with the antibodies bound to the glomerular basement membrane. After removal of these contaminants, the antibodies were linked to cyanogen bromide-activated Sepharose and used to affinity purify four antigenic fractions from the collagenase-digested glomerular basement membrane. These fractions were eluted by 0.2 Mglycine pH 2.8 and with 0.5 Mammonium thiocyanate and had molecular weights of 22–25,43–45,65–70 and 205 ×10<sup>3</sup> daltons. The smaller molecular weight components were shown to be common to both included and excluded fractions obtained by Ultragel AcA 44 chromatography of the digested material in 10 m M phosphate pH 8. This suggests that the larger molecular weight component would be an aggregate of a smaller component. Preliminary carbohydrate and amino acid analyses indicated that the different elution procedures elicited antigens with different chemical characteristics.