Abstract: A holder is selectively secured to the stage of a microscope for adapting the microscope to hold a test tube oriented horizontally between the microscope objective and a light source for microscopic examination of a biological specimen while retained in the test tube, thereby eliminating the necessity of preparing a microscope slide for the specimen. The holder includes a base assembled of slotted base plates selectively slidable relative to one another to be fitted to the microscope so as to establish a slot for retaining the test tube in registration with the microscope objective and the light source, and fasteners for fastening the base plates together in secure attachment to the stage of the microscope.