After another weekend reacting to tweets from Tesla boss Elon Musk, Bitcoin hit a two-week peak just shy of $40,000 on Monday (June 14).
Musk fended off criticism over his market influence.
And said Tesla might resume transactions using bitcoin.
The world's biggest cryptocurrency has fluctuated over Musk's views for months, not least since Tesla announced a $1.5 billion bitcoin purchase in February.
The electric car giant had also said it would take the virtual money in payment.
But Musk later back-tracked on that, citing concerns over how mining the currency requires high energy use and contributes to climate change.
On Twitter on Sunday (June 13) he said Tesla would resume allowing bitcoin transactions, when there's "confirmation of reasonable clean energy usage by miners."
The digital currency rallied more than 9% after that message.
Analysts said the market was also supported by software company MicroStrategy raising half a billion dollars to buy bitcoin.
The e-currency is up around a third this year.
But has collapsed from a record peak above $60,000 amid a regulatory crackdown in China and Musk's apparently wavering enthusiasm for it.