Shares of the North Huntingdon, Pa., company at last check surged 45% to $25.02. ExOne's 52-week high is $66.48, set in early February.
Desktop Metal, Burlington, Mass., was down 5.2% at $8.47.
Under the terms, Desktop Metal will pay a total of $192 million cash and $383 million of stock for ExOne.
The terms have been approved by ExOne's board. The deal is expected to close in the fourth quarter, subject to conditions including regulatory clearances and a vote of ExOne holders.
ExOne was founded in 2005 and has about 263 employees.
During the Lightning Round of Wednesday's "Mad Money," TheStreet's Jim Cramer mentioned Desktop Metal, saying, "I'm not going there. I don't like 3D printing."
Several analysts downgraded ExOne following the acquisition proposal. Stifel analyst Noelle Dilts downgraded ExOne to hold from buy with a price target of $25.50, down from $30, according to the Fly.
Benchmark.analyst Josh Sullivan said Desktop Metal will still have about $320 million of cash on hand after the acquisition, Bloomberg reported.
"We see the cash burn rate as manageable while several binder jetting technologies reach maturity, and with the XONE acquisition adding infrastructure as well as customers to accelerate that process," said Sullivan, who has a buy rating on Desktop Metal and a $22 price target.
"We believe this acquisition will provide customers with more choice as we leverage our complementary technologies and go-to-market efforts," Ric Fulop, founder and chief executive of Desktop Metal, said in a statement.
Separately, ExOne reported a second-quarter loss of 25 cents a share, matching the FactSet consensus. Revenue totaled $18.8 million, beating FactSet's call for $15.1 million.
Desktop Metal reported a loss of 8 cents a share, compared with FactSet's forecast for a loss of 10 cents a share. Revenue totaled $19 million, up by a factor of more than seven from a year earlier. FactSet called for a total of $19.2 million.