We have studied qualitative and quantitative changes of several parameters during chloroplast development in Spirodela oligorhiza (duckweed). On a dry weight basis, the amount of protein increases from 2.5% (w/w) in dark-grown to 7.8% (w/w) in light-grown fronds. At the same time the amount of starch drops from 50% to 27% (w/w). Using an immunochemical quantification method we have found that during greening of etiolated plants the amount of all subunits of the ATPase complex per frond increases 10-fold, whereas the level of the subunits of ribulose-1,5-biphosphate carboxylase increases 50-fold. Cytochrome f was found to be present in dark-grown Spirodela and the amount of this polypeptide per frond increases about 30-fold. The concentration of a polypeptide that possibly represents a cytochrome b6 subunit increases about 10-fold upon greening. The molar ratio of the CF1-beta and CF1-gamma subunits of the ATPase complex varies over 2-3, while in all stages of chloroplast development studied the molar ratio of the carboxylase subunits is about 1. As these values are in agreement with the stoichiometrical amounts in the native protein complexes, we conclude that the synthesis of CF1-beta and CF1-gamma, as well as the synthesis of the large and small carboxylase subunits, are strictly coordinated during chloroplast biogenesis in Spirodela oligorhiza.