When Google first passed Microsoft in terms of stock market value six years ago, it looked like the companies were headed in opposite directions.
But over the past 12 months, Microsoft has surged 40 percent, more than five times Alphabet's gain, and has again become the more valuable of the two. As of Tuesday's close, Microsoft was worth $749 billion and Alphabet's market capitalization stood at $739 billion.
Microsoft's latest rally has been sparked by growth in its cloud computing business, which is bigger than Google's though it still trails Amazon Web Services. In March, Microsoft reorganized its Windows and Devices Group and moved its engineering resources into other units, including one focusing on cloud and artificial intelligence.
Google went public in 2004 and spent the next eight years closing the gap with Microsoft, which debuted on the stock market in 1986. Even after Google first passed Microsoft in 2012, the companies flip-flopped several times over the next few years.
But Google, which created Alphabet as its parent company in 2015, took a commanding lead that year and held onto it until this month. Microsoft is now the world's third most valuable publicly traded company, behind Apple and Amazon. Alphabet is fourth, followed by Facebook and China's Tencent.
On Tuesday, Microsoft fell 0.4 percent to $98.01, while Alphabet's Class A shares dropped 1.5 percent to $1,068.07.