A procedure has been developed for the isolation of recombinant spider silk proteins based upon their unique stability and solubilization characteristics. Three recombinant silk proteins, (SPI)(7), NcDS, and [(SpI)(4)/(SpII)(1)](4), were purified by extraction with organic acids followed by affinity or ion exchange chromatography resulting in 90-95% pure silk solutions. The protein yield of NcDS (15 mg/L culture) and (SPI)(7) (35 mg/L) increased 4- and 5-fold, respectively, from previously reported values presumably due to a more complete solubilization of the expressed recombinant protein. [(SPI)(4)/(SPII)(1)](4), a hybrid protein based on the repeat sequences of spidroin I and spidroin II, had a yield of 12.4 mg/L. This method is an effective, reproducible technique that has broad applicability for a variety of silk proteins as well as other acid stable biopolymers.