The brattice window method was used to measure the leakage rates of 42 ventilation stoppings in 8 hardrock mines. Various types of stopping construction were evaluated. In order of decreasing effectiveness, the types evaluated are as follows: (1) cinder block, (2) timber and mortar, (3) timber and polyurethane foam, and (4) timber and brattice material. There are slight differences in the effectiveness of the first three types, while the timber and brattice type is substantially inferior to the others. The repeatability of the brattice window method varied with physical conditions in the mine such as stopping location with respect to intersections, regularity of drift cross section, and the presence of hardware such as air and water pipes, timber sets, and wire mesh. A laboratory test program resulted in the derivation of several "rules of thumb" for employing the brattice window method.