A big uptick in raw material prices helped two old-economy powerhouses boost their first-quarter earnings outlooks Wednesday.

DuPont ( DD) took up guidance dramatically, citing unexpected strength in its agriculture and nutrition segment and higher volume across its business lines.

And shares of Georgia-Pacific ( GP) were moving higher after the company said it expects first-quarter earnings to come in ahead of analysts' estimates, citing solid results from its building products businesses.

"These are coincident indicator-type companies," said Howard Simons, a trading consultant and contributor to RealMoney.com, a sister site to TheStreet.com. "You can definitely link them to the commodity rally."

Excluding one-time items, chemical company DuPont expects to earn 95 cents a share, up significantly from previous earnings guidance of 65 cents to 75 cents a share and the Thomson First Call analyst consensus of 73 cents a share. The company's stock was rising $1.21, or 2.8%, to $44.90.

Citigroup Smith Barney analyst P.J. Juvekar thinks most of DuPont's upside comes from a strong agricultural cycle; corn, for example, is at an eight-year high. Corn futures were lately up 1.75% at $319.5 a bushel and the price of corn closed at $311.75 a bushel on April 13, which is up from $226 a bushel on Oct. 21.

Juvekar also said DuPont buys large amounts of raw materials, especially paraxylene, a hydrocarbon aromatic compound. But because the company's supply chain is long, he doesn't think the prices will boost the company's bottom line for three to six quarters. (Citigroup does investment banking for DuPont.)

Simons noted that lower natural gas prices in January and February likely helped DuPont's quarter. "They're an economically sensitive company," he said. "If demand for products is strong, you can live through an increase in natural gas prices. That's what they've done here."

DuPont's first-quarter bottom line will include a charge of 14 cents a share to set-up a reserve for litigation involving DuPont Dow Elastomers, and a charge of 2 cents a share for an expected settlement of litigation involving its coatings and color technologies unit. DuPont also expects more adjustments related to its spinoff of Invista.

The company will report earnings April 27.

For the full year, DuPont expects to earn $2.10 to $2.30 a share before charges, up 10 cents a share from previous guidance. Analysts surveyed by Thomson First Call were forecasting earnings of $2.16 a share for the full year.

Meanwhile, Georgia-Pacific forecast earnings of 60 cents a share, compared with the 48 cents a share expected from analysts surveyed by Thomson First Call. The guidance excludes $26 million, or 6 cents a share, from early extinguishment of debt expenses.

Shares of the company were lately up 95 cents, or 2.8%, at $35.07, a new 52-week high.

"The story with Georgia-Pacific is the high price of wood products and the record-high oriented strand board (OSB) prices," said Stephen Atkinson, an analyst at BMO Nesbitt Burns. OSB is used in several applications in home building, including walls and roof panels. It is harvested from faster-growing trees, which makes it less expensive to produce.

In the first quarter, lumber and panel prices have risen quickly as the U.S. housing boom continues. The price of lumber closed at $414 per 1,000 board feet on Tuesday, which is up from $285 per 1,000 board feet on Oct. 22.

Merrill Lynch analyst Karen Gilsenan also thinks the increase in both lumber and plywood prices as well as an increase in demand are what drove the quarter, but she noted that the fundamentals of the company's other commodity businesses -- packaging and paper -- continue to improve. (Merrill Lynch does investment banking for Georgia-Pacific.)

Atlanta-based Georgia-Pacific will release quarterly results on April 29.