Zurich Financial Services, the Anglo-Swiss insurance giant, said earnings in the second half of the year were "not likely to reach the level achieved during the first six months".
The statement from Zurich, formed last week from the merger of Zurich Group with British American Financial Services, was echoed by Irish Life, the largest insurance group in Ireland.
Irish Life warned market weakness could wipe out gains made on roaring investment markets in the first half of the year, which helped boost operating profits by 40 per cent.
David Went, managing director of Irish Life, said sales looked set to continue their upward trend: "Sales performance in the second half looks set to continue the trends in the first half. However, our profitability is geared to the equity markets and the operating profit will be impacted by the course of investment markets since June.
"Based on current conditions this is likely to result in a reversal of much of the investment gains."
Like other investment firms, Irish Life charges for managing money by levying a fee as a percentage of the investment. When markets slump, fees will go down while overheads stay the same, creating the geared effect on profits.
The warnings may signal an end to the boom in financial services after a bumper six months between January and June, when booming markets created ripe conditions for the sale of financial products.
Zurich said its member companies - including Allied Dunbar, Eagle Star, Threadneedle Asset Management, Farmers and the existing Zurich - generated earnings of $1.42bn (pounds 0.85bn) in the first half.