By March 1956 a 50-pound bag of onions in Chicago sold for 10 cents, less than the burlap sack that held it. Seven months earlier the same bag had cost $2.75. The collapse was engineered. The Chicago Mercantile Exchange had turned to onion futures in the 1940s after its butter trade dried up, and by the mid-1950s onions made up 20 percent of its volume. In the fall of 1955, traders Sam Siegel and Vincent Kosuga bought 99.3 percent of the onions and onion futures in Chicago, about 30 million pounds, then told growers to buy the hoard or watch it dumped on the market.

The growers paid, and were betrayed. Siegel and Kosuga took large short positions and manufactured a glut on paper, shipping their rotting onions out of the city, repackaging them, and bringing them back to generate fresh warehouse receipts. This episode follows the fallout: bankrupt farmers, a bill sponsored by Michigan congressman Gerald Ford, and the Onion Futures Act signed by President Eisenhower in August 1958. It also covers what the ban did to the exchange, the long dispute among economists over whether it helped, and why the law is still on the books.

• Stripped of a fifth of its volume and defeated in court, the CME survived by inventing new contracts, including pork bellies and frozen concentrated orange juice.
• Economists Holbrook Working, Roger Gray, and Aaron C. Johnson reached conflicting conclusions on whether futures trading calms or worsens onion price swings.
• Journalist Justin Fox noted that calmer onion prices in the 1960s may owe more to interstate highways and refrigerated trucking than to the ban.
• In 2010, after lobbying from Hollywood, the act was amended to also bar futures on motion picture box office receipts.
• In spring 2026 a University of Chicago student group called For Our Futures handed out raw onions on the quad and collected 131 signatures for repeal, then 99 more at Northwestern.