The NPC1 and NPC1L1 are related genes whose general role is in cholesterol trafficking. However, reduction of activity of these genes results in very different phenotypes. Niemann-Pick C disease type 1 is a neurodegenerative disease with no current treatment, where cholesterol accumulates in lysosomes. The disease arises due to autosomal recessive mutations in the NPC1 gene. The NPC1L1 gene has recently been identified as the target for the drug ezetimibe (Zetia), a cholesterol absorption inhibitor, and has been shown to be an intestinal cholesterol transporter. We demonstrate that human NPC1L1, as well as human NPC1, can functionally substitute for the Caenorhabditis elegans genes ncr-1 and/or ncr-2. These genes are known to play a role in the process of dauer formation, a process which can be modulated by cholesterol in sensitized genetic backgrounds. Our results demonstrate that these human proteins retain some functional conservation, though their biological roles are vastly different.