在國際收支帳須符合跨期平衡的假設下，本文試圖尋求一個貨幣當局放棄固定匯 率制度的先期條件。當目前之政策違反跨期平衡，則未來之政策需要改變，匯率制度的改變 可能即為其一。 使用 Trehan and Walsh (1991) 所建立之測試跨期平衡假說的方法，推論 外匯準備成長率為非恆定是違反跨期平衡之充分條件， 我們研究 5 個國家及 12 個案例， 計算固定匯率制度崩潰前外匯準備成率之 Augmented Dickey-Fuller 統計量。 結果顯示， 在所有崩潰的案例中，崩潰前，跨期平衡並不成立，崩潰時，強烈的非恆定穩含投機性炒作 的發生，而固定匯率制度之崩潰與否，政府之政策決定是一個重要因素。

　　　　　Under the assumption that the balance of payments must satisfy the expected intertemporal balance constraint, this paper seeks to establish a pre-condition for the collapse of a fixed exchange rate regime. Whenever current policy violates the expected intertemporal balance constraint, we argue that future policy change, possibly including the exchange rate regime, is anticipated. Proposing that the non-stationarity of the growth rate of assets is evidence of a violation of the expected intertemporal balance constraint, we calculate Augmented Dickey-Fuller statistics for the growth rate of the foreign exchange reserves prior to separate crises in fixed exchange rate regimes. For most crises there is evidence of a violation of the intertemporal balance constraint prior to the month of the crisis.However, there are also periods, in which intertemporal balance constraints are violated, and in which the fixed exchange rate is not threatened.