The mature seeds of durian (Durio zibethinus L.) are recalcitrant, with the cotyledons storing both starch (amylose, 78% dry weight) and some protein (7%), but having few triglyceride reserves (<1%). Reserve accumulation occurs during the latter third of the 110-d seed developmental period prior to fruit shed. The storage proteins of durian seeds consist of two immunologically related unglycosylated albumins, light and heavy zibethinin (20.2, 21.4 kDa), that account for 37–46% of the total protein during development. Light zibethinin is a single polypeptide, most likely having internal sulphydryl linkages, whereas heavy zibethenin is composed of two sulphydryl-linked subunits. The zibethinins are deposited in swellings of the endoplasmic reticulum (ER) which then either expand or coalesce to form protein storage vacuoles. This mode of protein body formation in durian varies from both the ER–Golgi complex–vesicle–vacuole pathway characteristic of many dicotyledonous seeds and the direct ER to protein storage vacuole pathway involved in deposition of certain prolamins in cereal endosperm cells. Protein storage vacuoles in durian seed storage parenchyma never become fully filled, but contain only diffuse peripheral clumps of zibethinin protein. There is a 15% loss in starch, a precipitous loss of total protein, and a concomitant loss of the zibethinin storage proteins during the 5 d prior to fruit shed, suggesting that both reserve mobilization and germination has begun.