Phytosphingosine is a phospholipid. Phospholipids are a class of lipids and a major component of all biological membranes; sphingolipid metabolites, such as sphingosine and ceramide, are highly bioactive compounds and are involved in diverse cell processes, including cell-cell interaction, cell proliferation, differentiation, and apoptosis. Phytosphingosine is also one of the most widely distributed natural sphingoid bases, which is abundant in fungi and plants, and also found in animals including humans. Phytosphingosine is structurally similar to sphingosine; phytosphingosine possesses a hydroxyl group at C-4 of the sphingoid long-chain base. The physiological roles of phytosphingosine are largely unknown. Phytosphingosine induces apoptosis in human T-cell lymphoma and non-small cell lung cancer cells, and induces caspase-independent cytochrome c release from mitochondria. In the presence of caspase inhibitors, phytosphingosine-induced apoptosis is almost completely suppressed, suggesting that phytosphingosine-induced apoptosis is largely dependent on caspase activities.