A procedure for isolating spinach (Spinacia oleracea L.) leaf peroxisomes in 0.25 molar sucrose solution by Percoll density gradient centrifugation followed by removal of the Percoll by washing and centrifugation was established. The preparation contains more than 90% peroxisomes as intact organelles with no detectable chlorophyll or cytochrome oxidase contamination. The peroxisomes are stable at 0 to 4 degrees C or 25 degrees C for at least 2 hours.