Shares of JPMorgan Chase (JPM) and Wells Fargo (WFC) were down in early trading Friday as investors fretted that the gains in their mortgage businesses, which bolstered their bottom lines last quarter, may not be sustainable.

First-quarter net income at JPMorgan was $5.4 billion, or $1.31 per share, down 29% from $5.6 billion, or $1.28, a year earlier, hurt by double-digit declines in investment banking fees, debt underwriting fees and advisory fees. Revenue rose 6% to $27.4 billion. Analysts had expected profit of $1.13 on revenue of $27.4 billion. The difference in the per-share figures was the result of fewer shares outstanding.

Wells Fargo's profit jumped 13% to $4.02 billion, or 75 cents, from $3.57 billion, or 67 cents, a year ago. Revenue rose 20% to $21.6 billion. The results beat analysts' expectations for profit of 73 cents on revenue of $20.51 billion.

The improvement in both banks' mortgage business was remarkable. JPMorgan reported $2 billion in mortgage fees and related revenue, reversing a loss of $489 million a year earlier. Mortgage originations at Wells Fargo totaled $129 billion in the first quarter, up from $84 billion  a year earlier. The bank's mortgage banking noninterest income rose 42% to $2.87 billion. Whether the gains are sustainable is not clear.

Though foreclosures in March were near a five-year low, experts warn that a surge in foreclosed properties looms as more properties make their way through the process. Mortgage lenders reached a settlement with state attorneys general in February over claims that they took illegal shortcuts in how they conducted foreclosures. A forecast released earlier this year by Zillow projects that housing prices will drop 3.7% this year, down from a 4.7% decline last year.

The test for Wall Street continues over the next few weeks. Citigroup (C), a major mortgage lender, issues earnings April 16. Analysts expect earnings of $1 per share on revenue of $19.85 billion, little changed from a year earlier. Morgan Stanley (MS), whose mortgage business is under federal investigation, and  Bank of America (BAC), which has scaled back its mortgage lending, report April 19. Morgan Stanley is forecast to earn 42 cents, compared with 50 cents a year earlier, on revenue of $7.24 billion, down 5% from a year earlier. Analysts expect dismal results at B of A, with earnings of 12 cents, versus 17 cents a year earlier, on revenue of $22.51 billion, down 16.2% from the year-ago period. 

The banks won't be out of the woods for another year or two. Investors should stay clear of these shares for now.

Jonathan Berr does not own shares of the listed companies.