The accompanying illustrations show a modification I have made of Esmarch's anesthetic mask. The hoop wires are supplied with joints at the ring base, thus allowing the hoops to be folded on each other. This gives a flat instrument, which lends itself easily to packing into small compass. The modification was worked out owing to the fact that the ordinary surgical and obstetric bags contain too little room. Our modern armamentarium is bulky and economy of space is desirable. The instrument is simple, durable and compact.