The nearly $80 billion that was pulled from money market funds in April was the highest monthly total in 16 years.

While some of that has already reversed in typical May fashion, the size of the outflow had some discussing whether a more fundamental change might soon be in store for the money market fund business.

Money market funds reported net cash outflows totaling $78.734 billion for April, according to AMG Data Services.

In March there were $114.45 billion of net inflows, bringing the asset total to a record $3.4 trillion.

For the last week of April, AMG reported a record $61.328 billion of outflows from money market funds. More funds reported net outflows than in any week since December 2003.

Money market executives agreed a decline resulting from tax payments is typical in April, but AMG said, there were $33.452 billion of inflows in April 2007.

In the first week of this month, things have already started to rebound for the industry; when according to AMG money market funds reported $47.853 billion of net cash inflows.

"Basically, we had $150 billion flow out of money market funds over a three-week period, and then we have about $50 billion flow back into funds last week," said Peter Crane, the president of Crane Data LLC, a Westboro, Mass., company that tracks the money market industry. "This is pretty normal for the weeks following April 15."

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