Ets-1 is a transcription factor which belongs to the ETS family. Its mRNA is expressed in the embryo during normal development and also in tumors. In order to sort out functional Ets-1-binding sites among those present in gene promoters, we constructed an expression vector and designed a purification protocol for the production of the 440-amino-acid form of mouse Ets-1, based on heparin-Sepharose affinity and anion-exchange chromatographies. This protocol allows the purification of large amounts of pure recombinant protein as assessed by SDS-PAGE, C18 reverse-phase HPLC, amino-terminal sequencing, and mass spectrometry. The purified protein is recognized by specific anti-Ets-1 antibodies and binds to DNA ETS-binding sites.