Amazon.com Inc. had a great second quarter with record profit on sales that surged 28% to $30.4 billion, and a good part of its growth stemmed from its business-to-business sales.

Amazon doesn’t break out exact figures for Amazon Business, its B2B section at Amazon.com/b2b. But in its financial report for the quarter ended June 30, it said Amazon Business had more than 400,000 business accounts. That’s at least a 33% increase from the end of the first quarter in March, when it said it had more than 300,000 business accounts, and a 100% increase from the 200,000 accounts it reported as of the end of last year. In effect, that means Amazon Business is adding about 100,000 accounts per quarter.

Businesses set up accounts on Amazon Business to buy or sell. The total includes about 30,000 sellers.

Amazon says Amazon Business reached $1 billion in sales during its first full year of operation, after launching in April 2015 as the successor to AmazonSupply.com. Prentis Wilson, vice president of Amazon Business, said in an interview in May that Amazon Business was growing sales 20% month to month.

Unlike Amazon Supply, which featured only products sold directly by Amazon, Amazon Business is a marketplace that sells products from other companies as well as Amazon. Amazon Business is No. 37 in the B2B E-Commerce 300, which ranks companies on their annual B2B web sales.

To read more about Amazon’s second quarter report, click here: