To provide a means capable of being applied in general or used in a wide range in usual practice of clinical diagnosis of an endometriosis field.

This diagnosis method of endometriosis includes the steps of: (a) getting a sample of menstrual blood; (b) measuring a basal cell in the sample or (c) measuring at least one kind of typical gene product in a cell of basal endometrium in the sample; and (d) correlating a measured value in (b) or (c) with the diagnosis of endometriosis. Or this diagnosis method of endometriosis includes the steps of: (a) getting a sample of menstrual blood; (b) measuring a basal cell in the sample; (c) measuring the amount of gene product induced from a cell of a functional layer of the endometrium in the sample; (d) evaluating the relative amount of (b) to (c), and (e) correlating the relative amount (d) with endometriosis.