This marks March 2007 as a high-water point in American retirement savings, as retirement assets for 2006 amounted to $16.4 trillion, the Investment Company Institute reported today.

Individual retirement accounts and defined-contribution plans factored into the retirement-savings growth, with first-quarter IRAs growing to $4.4 trillion from $4.2 trillion and DCPs growing to $4.2 trillion from $4.1 trillion.

In other categories, totals remained unchanged from 2006: Government pension plans stood at $4.2 trillion in the first quarter; private benefit plans at $2.3 trillion; and annuities at $1.3 trillion.

Long-term funds—including equity, hybrid and bond mutual funds—remained the most widely used method of holding mutual fund assets, with 47 percent of investors using them as a retirement-savings method. Money market funds accounted for 13 percent of savings plans, and other funds represented for 39 percent, the ICI reported.

The institute is a national association of SEC-registered investment companies, advisors and underwriters whose mission is to advance the interests of and promote public understanding of mutual funds and other investment companies.

Filed by Sara Hottman of Investment News, a sister publication of Workforce Management. To comment, e-mail editors@workforce.com.