Pea(Pisum sativum) leaves were extracted with 20 mmol/L Tris-HCl (pH 7.8) at 4 ℃ containing 5 mmol/L mercaptoethanol. The extract was heated at 50 ℃ for 10 min, then centrifuged at 12,000 * g for 15 min. The supernatant was fractionated by 33% to 70% saturation (NH_4)_2SO_4. The precipicate was dissolved in a small volume, desalted with Sephadex G-50 column, and then loaded onto a DEAE-Sepharose fast flow column and then loaded onto a Sephacryl S-300 column. The BP peak fractions were collected. BP was examined by both ND-PAGE and by BP dissociation caused specifically by the addition of ATP. The yields of up t 20 mg/Kg fresh weight of leaves were obtained, which was 12-fold higher than the previous result. A highly specific anti-BP serum was prepared, which gave a single precipitin band with BP, by immunodiffusion tests, but no precipitin band with RubisCO. Western blot using antibodies to BP from pea detected subunits of closely similar size (61 kD or so) in the chlorophyte Chlamydomonas reinhardtii and filamental cyanobacteria (such as Anabaena siamensis), but in unicellular cyanobacteria (such as Anacystis nidulans) these homologous polypeptides couldn't be detected. These polypeptides were increased in amount under heat-shock conditions and decreased at lower temperature. We also found that BP from pea was a heat-stable protein and was easily dissociated at low temperature. This result assumes that homolog exist between BP from pea and groE-like chaperonins from algae both in protein structure and chacterizations. We provide evidence using electron microscopy coupled with antiserum to BP from pea and Protein-A colloidal gold. In filaments of Anabaena siamensis, groE-like chaperonin is absent from mature heterocysts and present well-distributedly in vegetative cells; in Chlamydomonas reinhardtii, groE-like chaperonin is present and it is associated both with pyrenoid and with thylakoid. Using Protein-A immunogold labelling technique, using antibody to RubisCO from rice, we found that in Anabaena siamensis, RubisCO is also absent from mature heterocysts, but present mainly in carboxysome in vegetative cells; in Chlamydomonas reinhardtii, RubisCO is mainly associated with pyrenoid.