Recombinant human TNF (rhTNF) was purified from cell extracts of cloned E. coli BL21(DE3)/pT7-TNF3,4 to apparent homogeneity by 80% ammonium sulfate precipitaion, DEAE-Sepharose ion exchange chromatography, and Sephacryl S-200 filtration followed by Bio-Gel P-100 gel filtration. The specific activity of this protein was increased approximately 30 fold during purification with an overall yield of 31%. In sodium dodecyl sulfate gel electrophoresis the recombinant human TNF migrates as a single band corresponding to a molecular weight of approximately 17 kDa. The molecular weight of the native protein as determined by Bio-Gel P-100 gel filtration was 48 kDa.