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Back up the truck, let the tailgate down, and load up... with biotech stocks. 

That might seem like bad advice with many biotech stocks still suffering after big drops over the last year. It's not, though. Now is a great time to buy some great biotech stocks. Here are three to seriously consider.

1. Amgen

Amgen (AMGN -1.82%) hasn't plummeted like some biotech stocks. On the other hand, shares haven't exactly taken off, either. Amgen's stock price is pretty much where it was a year ago. So what makes this big biotech worthy of investors' attention now?

For one thing, Amgen's top-selling drug, Enbrel, continues to perform very well. This autoimmune disease treatment chalked up sales of $5.4 billion in 2015. In the first quarter of 2016, sales grew at a strong 24% compared to the prior-year period, bringing in $1.4 billion in revenue. 

Up-and-coming drugs are also helping make Amgen's financial results look good. Eight other drugs in the biotech's current lineup posted double-digit percentage year-over-year sales increases in the first quarter.

The best news for Amgen, though, comes from its pipeline. Repatha won FDA approval last year for treating some patients with high cholesterol, but there's intense interest in the results from a phase 3 cardiovascular outcomes study that will be announced later this year. Analysts think Repatha could reach peak annual sales of at least $4 billion and perhaps much more than that.

Amgen has also made biosimilar development a big part of its development program. The biotech counts six biosimilars in its pipeline, including biosimilar versions of big-selling biologic drugs Humira and Rituxan.

Biosimilars, however, provide the most significant challenges for Amgen, as the company must also play defense to protect its own branded drugs' revenues. Neupogen already faces a rival biosimilar, and Amgen is trying its best to use legal procedures to fight off competition from a biosimilar for Neulasta.

2. Celgene

Shares of Celgene (CELG) are down more than 20% over the last 12 months. In my view, that drop presents a fantastic buying opportunity.

Like Amgen with Enbrel, Celgene's top drug keeps delivering strong growth. Revlimid raked in $5.8 billion in sales last year. The blood cancer drug started 2016 off with a bang, posting over $1.57 billion in sales during the first quarter -- a 17.2% year-over-year increase.

Also like Amgen, Celgene can claim several other fast-growing drugs in its lineup. Pomalyst/Imnovid and Otezla stand out as the biggest winners. It's possible that both drugs plus Abraxane could top the $1 billion sales mark in 2016, joining Revlimid in the blockbuster club.

Celgene's pipeline should add to the biotech's success in the not-too-distant future. Clinical studies are under way for additional indications for Revlimid, Abraxane, and Otezla. Celgene isn't limited to only making its current cash cows more profitable, though. Mongersen, which is in a late-stage study targeting Crohn's disease, and ozanimod, which is in a late-stage study for multiple sclerosis, could both generate annual revenue in the billions of dollars. 

Is there a weak link for Celgene? The only potential issue I see is if the federal government makes changes that force the company to slash prices on its drugs. That could happen, but it won't be just Celgene that will be affected if that's the case. 

3. Novavax

It's not just big biotechs that are buys right now. Novavax (NVAX -4.58%) only has a market cap of around $2 billion -- practically pocket change for Amgen and Celgene. There's a good case to be made for investing in Novavax, though.

Novavax doesn't have any products on the market yet. That could change relatively soon. Novavax expects to announce results from its phase 3 study of its RSV F vaccine in older adults within the next few months. The FDA has already granted "Fast Track" designation for the vaccine. Novavax predicts peak annual sales of $6 billion to $8 billion if approved.

If the phase 3 study results turn out to be positive, Novavax is trading at a dirt-cheap price right now. But could issues arise that derail the RSV F vaccine? It's certainly possible, but I think the chances are pretty good that the biotech wins approval.

Wall Street seems to agree. The average analysts' price target for Novavax represents an upside potential of almost 90%.