Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase; EC 18.104.22.168) was separated in extracts of plant leaves by capillary electrophoresis with replaceable polymers. Rubisco extracted fi-om plant leaves was fully denatured into small (15.8 kDa) and large (52.9 kDa) subunits in the presence of excess sodium dodecylsulfate (SDS). SDS-Rubisco complexes were separated by using an uncoated, fused silica capillary filled with a replaceable polymer solution, with detection at 220 nm. A calibration plot of Rubisco concentration in plant extract versus peak area was linear over the concentration range of 0.09-1.2 mg mL(-1) with a correlation coefficient (r(2)) of 0.995 and a detection limit of 0.05 mg mL(-1). The reproducibility of migration times was less than 0.27% RSD (n=5) and reproducibility of peak area was better than 6.9%. The recovery of Rubisco in leaf tissues through the extraction and analysis procedure was 78.2% (+/- 4.8) and through the analysis procedure alone was 96.9% (+/- 5.1). The proposed method was used for the quantification of Rubisco in protein extracts from leaves of a variety of plant species.