Shares in the trading platform Robinhood have surged, amid speculation the firm could be seeing the same frenzied trading that surrounded the video game retailer Gamestop.
The stock climbed as much as 82% on Wednesday, with trading paused several times due to wild price swings.
It follows a lacklustre stock market debut for the firm, which is popular with young investors but controversial.
Some bigger investors have shunned the company for being too risky.
Robinhood's commission-free trading has proved hugely popular with amateur traders during lockdown, with the number of account holders doubling to 31 million since January.