Money market mutual fund assets leaped 3.8%, to $933.22 billion, in the week that ended Jan. 8, the Investment Company Institute reported. from 899.22

The jump of $34 billion was the biggest ever reported in a single week, according to the Washington-based trade group. It was in keeping with seasonal trends.

Money fund balances usually fall sharply at yearend, then rise rapidly as investors park bonuses and cash gifts into these types of funds. This year's increase was also fueled by institutional money managers that transferred money from money market instruments with declining yields into funds.

Indeed, the inflows were concentrated in money market funds for institutional investors. Balances of these portfolios climbed 6.6% in the week, to $309.45 billion. That includes $277.91 billion in taxable portfolios, up 6.5%; and $31.54 billion in tax-exempt funds, up 7.7%.

On the retail side assets surged 2.5%, to $623.77 billion. Taxable funds held $507.81 billion, up 1.9%, while tax-exempt portfolios held $115.96 billion, up 5%.

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