Chloroplast proteins, 37-38 kDa, from barley were partially purified by ammonium sulfate precipitation followed by heparin agarose chromatography. The binding of these proteins to the in vitro transcribed chloroplast psbA mRNA was established by UV cross-linking assay and SDS-PAGE electrophoresis. A relatively simple protocol for in vitro transcription of psbA mRNA and purification of the chloroplast proteins which bind to this mRNA is described.