The hunt for growth never ends, and it often leads investors to unlikely places. Sometimes the best businesses to own are the ones quietly competing in markets you've never thought about, selling products you'd likely never directly need. 

And that just might be the case with a pair of great companies making chemicals, analytical kits, and hardware for use in life sciences laboratories. Given their recent performance, it's safe to say that both are monster growth stocks -- and if you're willing to buy them hand over fist, you'll be doing your portfolio a favor. Let's take a closer look at each to see why that's the case. 

1. Thermo Fisher Scientific

With its shares burgeoning by more than 959% over the last 10 years, obliterating the market's return of around 260%, Thermo Fisher Scientific (TMO 0.66%) might seem like an improbable contender for being an ultra-growth stock at first glance. Its primary line of business is selling instruments, supplies, and other laboratory hardware to life sciences companies, and it also sells diagnostic tests to hospitals and clinics. That means for every need it can anticipate and address for its customers in biotech and pharma, it makes money, and in 2021 it reported above $39.2 billion in revenue -- vastly more than the $18.2 billion it made in 2016.

Management expects that the company will continue to organically grow its core revenue at a rate between 7% and 9% each year, which is actually fairly slow for a growth-phase business. To get around the fact that its laboratory consumables and analyzer devices typically aren't needed by customers in significantly larger quantities each year, Thermo is an acquisition superstar, making nine major purchases since 2011. It intends to keep deploying as much as 75% of its capital on merger and acquisition (M&A) activity, thereby driving bolt-on top-line growth even in the absence of organic sales. Given its prior success with that strategy, it'll likely be a good one for it to continue. 

The company is also excellent at increasing the efficiency of its operations over time, thereby delivering consistent earnings. Its adjusted earnings per share (EPS) grew with a compound annual growth rate (CAGR) of 20% between 2011 and 2021, buttressed by rising revenue and new product launches. Some have even called the stock recession-proof as a result of its steamroller-like advance regardless of economic conditions. As long as management keeps executing on Thermo's business model like it has been over the last decade, people who buy the stock today will benefit from its uninterrupted forward march, and there's little to prevent it from continuing to flourish. 

2. PerkinElmer

In many ways, PerkinElmer (RVTY -0.09%) is a smaller version of ThermoFisher, as it makes diagnostic tests, life sciences reagents, and laboratory analyzer devices. Over the last five years, its shares grew by 440%, and there's reason to believe that it can continue to rise. PerkinElmer's business focuses more on offering consumable products like experiment kits, which is how around 80% of its revenue is recurring. It predicts that it'll bring in $3.3 billion this year, and management claims that its long-term organic revenue growth rate will be in the ballpark of 10%. For reference, over the last three years, it grew its trailing-12-month (TTM) revenue by 77.1%, which isn't half bad.

In terms of its market positioning, PerkinElmer holds the largest share of the market for autoimmune and reproductive health diagnostics. It also has the third-place spot in the market for DNA and RNA extraction kits, which is critical because practically every biomedical laboratory in the world has an ongoing need for such products. To top it off, it's additionally the leading provider of pharmaceutical services among the 20 largest companies in the industry.

When paired with the fact that most of the sales it makes will recur once its customers consume all of what they purchased, its organic growth rate and market leadership make the company's expansion start to look quite robust over a few years' time, and that's one of the biggest reasons to buy the stock. Maintaining its market shares will also help to keep its base of recurring revenue rising year after year, as will developing new products based on new trends in biomedical research. And in the long run, that'll pay off big for investors who start a position in the stock today.