This has definitely been the year of the acquisition for large-cap pharma corporations, which have been buying out smaller companies like crazy to make up for slowing sales growth and drugs going off patent. The European pharmas have been particularly busy this year, with several multibillion-dollar acquisitions. The biggest of them all has been Bayer's (NYSE:BAY) $20 billion buyout of fellow German pharmaceutical firm Schering AG.

Bayer revealed the effects that Schering's products have had on its financial results when it announced its third-quarter financial results on Monday. Overall sales were up 26% to $10.1 billion (at a $1.3 dollar-to-euro exchange rate), but much of that growth was due to the acquisition. Excluding Schering's operations, Bayer's revenues were up a much more modest 3% over the third quarter of 2005.

Sales from Bayer's health-care division came in at $4.5 billion, but excluding the Schering acquisition, they were only up a measly 3%. Even absent Schering's contribution, earnings growth from this division was much better, though. It grew nearly 19% to $640 million as Bayer's health-care EBITDA margins jumped 25% higher than the 20% margins seen in the third quarter of last year.

If Bayer can stick to its planned $900 million in expected annual synergies from the Schering acquisition, and if most of these cost reductions and other optimizations occur in the health-care division, then that means there will be plenty of future earnings growth from this division for quarters to come, even if sales growth doesn't return.

Revenues for the health-care division should improve, though, as Bayer's top-selling drugs -- the multiple sclerosis treatment Betaseron and the birth control pill Yasmin -- both had sales growth at double-digit rates in the third quarter. Eventually, they're expected to outgrow the losses experienced by other drugs facing generic competition.

An investment in Bayer is obviously not only about how well its health-care division performs, but with the Schering AG acquisition, the two components of its health-care division (pharmaceuticals and consumer health products) have risen to account for almost 45% of overall sales and have also become the main earnings growth driver for the company. With overall total sales stagnating, however, Bayer's future success is somewhat leveraged to the synergies, cost reductions, and subsequent margin improvements that will come as a result of the Schering buyout. So it's not time to jump on the Bayer bandwagon just yet.

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Fool contributor Brian Lawler does not own shares of any company mentioned in this article. The Fool has a disclosure policy .