The Hong Kong Futures Exchange Clearing Corp collected $456 million in margin calls from futures brokers yesterday to cover their loss-making positions. Margin calls are a risk-management measure taken during times of market volatility. The exchange asks all futures brokers to put in deposits to cover loss-making positions in the futures contracts they are holding. An exchange official said the exchange collected $17 million in margin calls for Hibor futures in yesterday's morning session. In the afternoon, the exchange collected another round of margin calls of $439 million from brokers to cover loss-making positions held in Hibor and Hang Seng Index futures. 'The margin calls have been collected smoothly, and all futures brokers could pay them quickly,' the official said. She said the exchange would continue to monitor the market and collect further margin calls as soon as required. A Securities and Futures Commission official said the commission would monitor the financial situation of all stock and futures brokers as usual in a bid to ensure all brokers were financially healthy during the market downturn.