Sometimes the best industries are also the biggest.

From health to media to environmental services, companies that landed atop the 2017 Inc. 5000, a list of the fastest-growing private companies in the U.S., amassed more than $206 billion in sales, up from $199 billion in 2015. But not everyone can make the big bucks.

Amid Inc.'s annual tally here are the fast-growing industries--as measured by 2016 revenue, the latest full-year for which information is available--that also double as the biggest revenue drivers.

5. Construction

Business owners are proving that one of America's oldest industries is by no means antiquated. In fact, private companies in the construction sector have built their way to as much as $13 billion in annual revenues, according to results of the 2017 Inc. 5000, up from $12.8 billion in 2015. Adam Hergenrother, the founder and CEO of BlackRock Construction, can attest to the industry's growth. At his South Burlington, Vermont-based company, sales grew by 6,611 percent between 2013 and 2016, booking $14.4 million last year alone. This year, BlackRock landed atop Inc.'s list at No. 42.

4. IT Services

Nagarjun Gandu, the CEO of Plano, Texas, IT firm Spar Information Systems, grew sales by more than 9,114 percent between 2013 and 2016. His business, which provides data processing and storage services, generated $19.1 million in 2016--garnering the 30th slot on this year'sInc. 5000. Its industry--that is, IT services--overall accounted for as much as $15.3 billion in revenues, down slightly from 2015, when it generated $17.1 billion in sales. This year, IT represents 599 companies on the list--the most of any sector, by far.

3. Financial Services

Companies that aim to manage, process, and store currency are also some of the largest revenue generators. In 2016, financial services on the Inc. 5000 accounted for $17 billion in sales, compared with $14.5 billion in 2015. That includes companies such as Small Business Owners of America, a Columbus, Ohio-based lending firm that provides short-term financing for businesses, as well as services such as incorporating and drawing up business plans. Headed up by CEO James Moore, Small Business Owners of America booked $19.7 million in revenue last year, up 19,352 percent from 2013. It ranks No. 6 on the Inc. 5000.

2. Business Products and Services

They might not sound sexy, but B2B firms have been reeling in massive sales over the past three years, according to Inc.'s list. Collectively, these companies booked $19.2 billion in 2016 revenues, up from $18.9 billion in 2015. Take the Chicago-based GrowthPlay, which consults with businesses on issues such as staffing and branding. Under CEO Dan Weinfurter, GrowthPlay generated some $29.3 million in 2016 sales, up 9,934 percent from 2013. That landed it on the Inc. 5000at No. 22 this year.

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1. Health

Even as the future of healthcare remains in flux--as the Trump Administration works to make good on the President's campaign promise to repeal and replace the Affordable Care Act--private healthcare providers have seen a surge over the past three years, according to the 2017 Inc. 5000. In total, health services brought in $25 billion in sales last year, up from $21.5 billion in 2015. Consider addiction recovery service provider Adva-Net based in Lakewood Ranch, Florida. The business grew its sales by 13,462 percent between 2013 and 2016, ranking No. 13 on Inc.'s list. Adva-Net brought in $24.4 million in sales last year.