Membrane roof of the stadium in Pontiac, Michigan, completed in 1976, is reported to be the largest air supported structure yet constructed. The 35 000 m**2 roof of pfte-coated glassfiber is supported by 18 restraining cables and encloses seating for 80,600 spectators. The original open-roof design was modified by the incorporation of a compression ring, and the plan shape adjusted from 45 to 37 degree corners. The method of erection is described.