Assets invested in money market mutual funds rose 0.3%, to $596.4 billion, in the week that ended Aug. 3, the Investment Company Institute reported.
The gain, from $594.64 billion the prior week, was fueled primarily by institutional investors.
Assets of the 284 institutional money market funds climbed by $1.23 billion in the week, to $173.7 billion.
Within that category, the 229 taxable funds picked up $358.6 million, closing at $151.52, while the 55 tax-exempt funds drew $872.4 million, to total $22.17 billion.
The picture was mixed on the retail side.
Total assets of the 672 retail money market funds climbed $526.5 million, to $422.7 billion.
But balances of the 417 taxable funds fell $84.6 million, to $330.12 billion.
The 255 tax-exempt funds attracted $611.1 million, closing the week at $92.59 billion.