BACKGROUND: Solubilization of inclusion body (IB) proteins by conventional methods (i.e. high concentrations of denaturants such as chaotropes) is a challenging process due to denaturation of the native-like secondary structures and subsequently low recovery into bioactive forms. The main objective of this work was to study the effect of a range of chemicals at low and very low concentrations on the solubilization of IB proteins produced in Escherichia coli and the enhancement of the target protein biological activity subsequent to refolding. RESULTS: Performance of chemical combinations at low and very low concentrations through the solubilization process of recombinant streptokinase (rSK) from IBs isolated from E. coli was appraised based on values pertinent to three parameters including target protein solubilization yield, purity and biological activity. In comparison with the conventional IBs' solubilization method (i.e. 4 mol L-1 urea), combinations of 0.5-1 mol L-1 urea with very low to low concentrations (0.05-1%) of detergents resulted in considerable target protein solubilization (by 100%), very high post-solubilization target protein purities (up to 100%) and biological activities (up by 360%). CONCLUSION: Owing to the improvements in the abovementioned integral parameters, these chemical treatments are good candidates to be considered for more efficient and cost-effective recovery of recombinant target proteins from IBs. (C) 2017 Society of Chemical Industry