Neutrophils and spleens were prepared from mice after treatment to induce amyloid deposition. The deposition of amyloid was accelerated in normal recipients by intravenous injection of more than 2 x 10(4) neutrophils, and intraperitoneal injection of supernatants obtained by homogenization and centrifugation of the neutrophils and spleens. The supernatants were subjected individually to DEAE ion-exchange chromatography. Amyloid enhancing factor (AEF) activity was present in peaks eluted at an NaCl concentration of 0.17 M. The fractions containing AEF were subjected to high-performance liquid chromatography (HPLC), and AEF was eluted at a position corresponding to about 15 KDa. Purified AEF was analyzed by amino acid sequencing and gas chromatography. The N-terminal amino acid was blocked, and AEF contained some saccharides including glucose, mannose, galactosamine and sialic acid, and an undefined substance (probably derived from certain proteins). Immunoelectron microscopy by the pre-embedding method using an anti-AEF antiserum demonstrated that the cytosol, but not primary and specific granules in neutrophils from the spleen of amyloid-laden mice, reacted with the antiserum. These findings suggest that AEF is a glycoprotein associated with neutrophils.