Experimental amyloidosis was induced in mice with repeated injections of complete Freund's adjuvant (CFA) reinforced with bacterial vaccine. BAPN administered in a mixture with CFA or on its own before the injection of CFA reduced the incidence of amyloidosis. The reduction in the incidence of amyloidosis following the administration of BAPN may be due to its inhibitory effect on the oxidative deamination of amino acids, which presumably inhibit cross-linking of amyloid fibrils or interfere with metabolic pathways which involve the formations of mucopolysaccharide formation. It is suggested that the defective formation of the mucopolysaccharide-amyloid protein complex inhibits amyloid deposition and induces the activity of beta glucuronidase observed in the present study. The reduced incidence of amyloidosis following BAPN adminsitration cannot be due to lysosomal enzyme degradation of the amyloid as the activity of cathepsin D and acid phosphatase is decreased during this process.