Abstract: A sterility indicator device comprising a base of steam permeable, absorbent material, e.g. paperboard, having mounted thereon at least one, though preferably three separate indicator ink spots of chromium chloride that change color in response to predetermined combinations of time, temperature and saturated steam, impermeable transparent cover films bonded to the top surface of the base overlaying the indicator ink spots and to the bottom surface of the base thereby preventing the escape of corrosive reactants there through, and an adhesive substance, to be used to bond the impermeable cover films to the base.