(Corrects fall of Volkswagen share price in first bullet point and second paragraph)
* Volkswagen down as much as 22.8 pct on U.S. emissions scandal
* FTSEurofirst 300 and Euro STOXX 50 both up more than 1 pct
* Dialog down 17 pct after deal to buy Atmel
* Europe bourses in 2015: link.reuters.com/pap87v
* Asset performance in 2015: link.reuters.com/gap87v
By Danilo Masoni
MILAN, Sept 21 (Reuters) - European shares rebounded on Monday, buoyed by stronger healthcare, bank and chemical stocks, although a slump in carmaker Volkswagen held back the German market.
Volkswagen shares fell as much as 22.8 percent, their biggest ever one-day fall, on news that Europe's largest carmaker had rigged U.S. emissions tests, and Germany said it would investigate whether data had been falsified in Europe too.
Volkswagen launched an investigation into the matter and could face penalties of up to $18 billion, said the U.S. Environmental Protection Agency (EPA).
"The commencement of legal proceedings against VW by the U.S. EPA is profoundly serious," Bernstein wrote in a note.
The drop in Volkswagen affected other auto stocks, with BMW and Daimler down over 1 percent, while Germany's DAX rose 0.5 percent, underperforming its European peers.
The pan-European FTSEurofirst 300 index and the euro zone's blue-chip Euro STOXX 50 index were up 1.1 percent and 1.4 percent respectively.
Traders said European equities were rebounding from last week's losses triggered by the U.S. Federal Reserve's downbeat comments last week about the global economy, yet the underlying trend remained uncertain.
"There still isn't a clear direction. European indexes still need to gain at least a couple of percentage points to give a positive signal," ActivTrades chief market analyst Carlo Alberto De Casa said.
Sentiment on Monday was helped by Sunday's clear election outcome in Greece.
The broader European equity markets were underpinned by firmer healthcare, banking and chemical shares, while Wall Street opened higher, giving back some of their big losses last week.
Bayer advanced 2.6 percent after the chemicals company's plastics division Covestro said it aimed to raise about 2.5 billion euros in an initial public offering.
Spanish bank Santander rose 0.5 percent after Citigroup upgraded the stock to "buy" from "neutral".
But Dialog Semiconductor fell 17.7 percent after the microchips maker agreed to buy U.S. peer Atmel for $4.6 billion.
Greece's stock market fell 0.6 percent after the leftist Syriza party's election victory, with yields on government paper edging lower. Investors' focus turned from the election to the formation of the new cabinet and the implementation of the country's third bailout.
The main Athens equity index ATG is down nearly 20 percent since the start of 2015, underperforming a 3 percent gain on the FTSEurofirst.
Today's European research round-up (Reporting by Danilo Masoni; additional reporting by Sudip Kar-Gupta in London; Editing by Dominic Evans and Kevin Liffey)