Construction of the Portland Cement Association's new Structural Laboratory gives a glimpse of some probable future practices in concrete construction. As would be expected, the Association made use of the most advanced current practice in concrete design, plus a few especially noteworthy innovations. As a laboratory, the structure is unique and may well have a revolutionary effect on future structural testing laboratories. From a engineering standpoint, the most interesting portion of the building is the testing floor which is a large hollow box girder 12 feet deep, 56 feet wide and 120 feet long. Designed by bridge design methods, the floor is capable of withstanding test forces greater than 10 million pounds. The top surface of the floor is pierced by 690 holes on 3 foot centers. Most test forces are applied by hydraulic jacks on the underside of the top floor surface. These jacks pull on steel rods which extend through the holes in the floor and are attached to test specimens above. This design makes the building an extremely flexible testing machine. An indication of its capabilities can be gained from the following figures: a floor or roof slab can be subjected to local stresses of 30,000 pounds per square foot; a slab the size of the entire test floor could be subjected to a load of many thousands of pounds per square foot; and a 50 foot beam can be subjected to a load of 2 million pounds. Because this laboratory has capabilities unmatched by any other facility in the world, it is expected to produce data having important effects on design of all types of concrete structures. Initial testing is aimed at improving connections between precast concrete elements, developing methods of achieving continuity between prestressed concrete units, and improving design of various types of concrete floor systems. A program has also been undertaken to develop needed engineering information on concrete shell roofs.