Optimism among U.S. millionaire investors rose to its highest level in six months in October, as a record-breaking run-up in the Dow Jones industrial average boosted optimism about the stock market, a report showed Wednesday.

Spectrem Group said its Millionaire Investor Index rose 2 points in October to 15, building on the previous month's reading of 13.

The company said its Affluent Investor Index, which measures households with $500,000 or more in investable assets, rose to 7 in October from a reading of 6 in September, but it's still in neutral territory.

Steady interest rates and a drop in oil prices added to optimism among wealthy investors, according to George Walper, Jr., president of Spectrem Group.

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"The environment in October seemed an ideal mix for investor optimism," Walper said in a statement. "Yet both groups appeared cautious, perhaps waiting to see if the good economic and market news is going to continue."

Looking forward, about 18 percent of the investors polled said stock market conditions were the biggest factor impacting their investment plans. Ten percent said the biggest factor was the economic environment, eight percent cited retirement and just 4 percent cited housing and real estate.

Spectrem's Affluent Investor Index polls 250 investors each month, while its Millionaire Investor Index takes responses from a subset of about 100 investors.

Copyright Reuters 2006.

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