Such unlikely elements as 5,000 rubber balls and 30,000 ordinary tin cans have played a roll in what is believed to be the first acoustical treatment of a thin-shell concrete ceiling in this country. The work involved an entirely new acoustical engineering technique developed just for a new $2 million ballroom and exposition hall for the Chase Hotel in St. Louis. The tin cans and the rubber balls were used as the most practical and economical means of casting 30,000 2- inch diameter holes clear through the 3- inch thick reinforced concrete ceiling. One of the striking features of the perforated treatment is that it accomplishes the integration of acoustical treatment with thermal insulation. In this case fibre-glass insulation placed between the ceiling and the protective roof covering also serves to absorb low-frequency sounds passing through the 30,000 holes in the concrete. The perforated ceiling is also reported to be strikingly attractive.