It is intended to provide a rapid, simple and noninvasive novel in vivo method for determining phospholipidosis (PLsis) by detecting a PLsis marker gene. More specifically, it is intended to provide a method for determining phospholipidosis in a mammal comprising the step of detecting change in expression of one or more genes whose expression changes correlated with the onset of phospholipidosis in a sample collected from the mammal, in which at least one of the genes comprises a base sequence identical or substantially identical to the base sequence represented by any of SEQ ID NO: n (wherein n is an odd number between 1 and 57, an integer number between 59 and 63, an even number between 64 and 98, 100 or 101.)