The life sciences investment teams of Morgenthaler Ventures and Advanced Technology Ventures are leaving their respective firms, Fortune has learned from multiple sources. The two groups will merge to form a new firm, with plans to begin raising a new fund by early next year.

For Morgenthaler, this is really the natural evolution of a process that began several years ago. When originally formed, the firm invested in both venture capital and general private equity out of a single fund. In 2007 it raised a $400 million fund to invest in venture capital, while the PE team kept operating as a quasi-independent entity (it has not yet raised a new fund, but still plans to try).

Even within the VC group, however, there were separations. For example, Morgenthaler’s IT and healthcare investment teams each benchmarked themselves against other IT or healthcare funds, rather than against general funds.

A decision was eventually made for the IT and healthcare venture teams to each raise separate funds, with the healthcare team expected to go out first (it had committed its allocation faster than had the IT team, which plans to raise its own fund next year). In early discussions, some of the Morgenthaler healthcare investors learned that their counterparts at ATV were talking about a cleavage from their IT colleagues, thus leading to the merger talks.

The first point of contact remains unclear, but Morgenthaler and ATV have co-invested in a number of deals. Most notable was Ardian, a Mountain View, Calif.-based maker of catheter-based therapies for hypertension, which was sold earlier this year to Medtronic (MDT) for $800 million in cash plus possible earn-outs that could push the deal past $1 billion.

The ATV partner on that deal was Mike Carusi, who also recently sold cancer drug developer Plexxikon to Japan’s Daiichi Sankyo for up to $935 million. He will be among those leaving ATV, alongside fellow healthcare partner Jean George. It’s currently unclear if fellow partner Tom Rogers and ATV’s three healthcare-focused venture partners also are joining the new group (at least five Morgenthaler pros are joining, and possibly more).

Earlier this year, ATV dismissed all investment staff below the partner level. At the time, Carusi told Fortune that ATV’s $300 million eighth fund was just under 60% committed, which meant the bi-coastal firm would begin raising a successor fund of similar size in the next 12 to 18 months. It is unclear if the remaining ATV team still plans to raise its own fund.

Also unclear is what will happen to the existing life sciences portfolios at Morgenthaler and ATV, although one source says to expect the departing teams to continue managing their legacy investments.

A Morgenthaler spokeswoman declined comment, while messages left for ATV’s Silicon Valley office have not yet been returned (no receptionist is answering at ATV’s Boston-area office, and its dial-by-name system is busted).

Update: Carusi declined to comment, except to say the East Coast phone issue was likely because the firm was moving its office from the suburbs into downtown Boston.

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