Tumour necrosis factor-alpha (TNF-alpha) is one of the cytokines that stimulate the production of serum amyloid A (SAA), the precursor of AA amyloid. The role of TNF-alpha in amyloidogenesis was investigated in experimental hamsters using purified recombinant human TNF-alpha (rhTNF-alpha) and rhTNF-alpha analogue different from the normal molecule by two amino acid substitutions. Daily injections of 1 mug rhTNF-alpha resulted in elevated SAA levels but even in the presence of amyloid enhancing factor (AEF) no amyloid was deposited, indicating that apart from the AEF and one particular SAA stimulating factor an additional factor is needed to result in amyloid deposition. This factor is generated by repeated injections of E. coli lipopolysaccharide (LPS). A single intraperitoneal injection of 12.5 mug or more of rhTNF-alpha followed by seven daily subcutaneous injections of LPS resulted in enhanced amyloid deposition. Heat denaturation of rhTNF-alpha did abolish its AEF activity. The rhTNF-alpha analogue, having one-fifth of the cytotoxic activity of the normal rhTNF-alpha, showed a similar reduction in its SAA-inducing capacity and its amyloidogenicity. This suggests the AEF activity to be closely related to TNF-alpha activity. However, poly(I).poly(C) (a potent inducer of IL-6) also showed AEF activity, suggesting that not a single cytokine but rather a certain combination of different cytokines could be decisive in AA amyloidogenesis.