Maltose binding proteins (MBPs) are used as carriers for improving the solubility of passenger proteins. Our results indicate that the higher solubility of the fusions correlates with their elevated heat stability. Fusions of the otherwise thermo-sensitive GFP with MBPs from Archaea, but not GST-GFP and Escherichia coli MBP-GFP, maintained their fluorescence and structure after 10min incubation at 100 degrees C and could be purified by heating the bacteria lysate, with yields even higher than those obtained using metal affinity chromatography. Furthermore, only correctly folded proteins could stand the heating treatment and, therefore, the heat-purification method can be used as a quality control step to select homogeneous monodispersed material whereas soluble aggregates are removed by precipitation.