Volkswagen shares are on a tear.
The auto giant's stock surged has by around a fifth just this week, and was up as much as 9% (March 18) on Thursday alone.
It later pared some of those gains, but remained close to 6-year highs.
Germany's market regulator is watching.
A spokeswoman for the BaFin agency said it was monitoring the move, in a 'routine way'.
But she didn't elaborate on what that meant.
VW shares have surged more than 50% this year, helped by raft of recent announcements.
Only this week, the firm lifted its target for electric vehicle sales, and said it would build six big battery factories.
It's all part of a drive to challenge Tesla in the market for zero-emission cars.
Barclays analysts say institutional and retail investors have warmed to the stock as a result.
The share price surge has lifted VW's market value above 160 billion dollars.
That has made it the most valuable firm on Germany's DAX index, ahead of software maker SAP.