Human native antithrombin (AT) can be converted to a partially denaturated form of AT, known its latent AT (L-AT). This latent form of AT has been shown to exhibit strong antiangiogenic activity and also to suppress tumor growth in mice models, In the present work, a method is presented which induces the conversion of native AT to L-AT. using incubation at 60 degreesC, for 16 h, with 0.9M ammonium sulfate, in 5 mM Hepes buffer, pH 7.4, giving a recovery of more than 70%. L-AT as determined by integration of the low heparin affinity peak when analyzed by the affinity chromatography method. Native polyaerylamide get electrophoresis was used to show that the preparation contained no aggregates. Hydrophobic interaction chromatography was also used for the separation of AT and L-AT. (C) 2002 Elsevier Science (USA). All rights reserved.