1. Spinach leaves contain a "Spinach Protein Factor" (SPF) which increases light sensitivity of colloidal chlorophylls in aqueous solution (Terpstra, 1967). SPF activity, measured in different fractions of spinach-leaf acetone-powder extracts obtained by gel filtration on DEAE- and CM-Sephadex, runs parallel with chlorophyllase activity. The same positive correlation is generally observed in aqueous extracts of certain small particles isolated from spinach-leaf homogenates. It is suggested that SPF is a chlorophyllase. 2. Another, less active chlorophyllase was found in endive leaves. Evidence is presented that this chlorophyllase competes with the more active SPF chlorophyllase for available (bacterio)chlorophyll. The less active chlorophyllase is also present, in varying amounts, in spinach leaves. 3. SPF activity and chlorophyllase activity are influenced by phosphate in different concentrations in a similar way. 4. Both the SPF chlorophyllase and the less active chlorophyllase accelerate the conversion of colloidal bacteriochlorophyll from a form with red absorption bands at about 845 and 790 nm into a form with a main red band at about 775 nm; besides, the chlorophyllases cause the 775 nm band to be shifted to shorter wavelength (770-766 nm). The conversion by the less active chlorophyllase is inhibited by Ca(2+) (0.01 M). Light sensitivity of the 770-766-nm bacteriochlorophyll form is enhanced by the SPF chlorophyllase, but not by the less active chlorophyllase.