Body fluid is sampled from a skin incision by placing a ring against the skin and repeatedly applying an elastic pressing force to the ring, whereby a stimulator surface of the ring depresses a ring of skin and body tissue in surrounding relationship to the incision to force body fluid from the incision. The stimulator surface is inclined at an angle of 10 to 65 degrees; a width of the stimulator surface is from 5 mm to 20 mm, and an inner diameter of the stimulator surface is no less than 6.0 mm.