Cellular transport of lysosomal enzymes: an alternative hypothesis

Hickman & Neufeld [(1972) Biochem, Biophys. Res. Commun. 49, 992-999] have proposed that lysosomal enzymes reach the lysosomes by means of exocytosis and subsequent pinocytic reincorporation. The results leading to this conclusion are re-assessed and an alternative explanation is advanced that relates to the necessity for membrane recycling in endocytic cells.