Assets invested in money market mutual funds fell 0.32%, to $621.15 billion, in the week ended Nov. 30, the Investment Company Institute reported.
The decline, from $623.19 billion the previous week, was concentrated in funds for institutional investors.
Balances in these funds dropped to $177.44 billion, down $2.46 billion.
Taxable funds for institutional investors held $154.12 billion, a decline of $2.51 billion. Tax-exempt funds held $23.32 billion, a $47.7 million gain.
On the retail side, money market assets grew to $443.72 billion, a gain of 427.5 million.
The retail total includes $349.61 billion in taxable funds, up $561.7 million for the week, and $94.1 billion in tax-exempt funds, down $134.2 million.