House prices increased slightly during May in the Altos Research 10-City Composite Price Index. May's 0.2% increase in median sales prices of single-family existing homes was the first positive month-over-month increase in nine months. The 10-city composite put the median sales price at $478,083 for homes in Boston, Chicago, New York, Los Angeles, San Diego, San Francisco, Miami, Las Vegas, Washington DC and Denver, compared to a median of $477,167 for the same markets during the month of April. The 10-city composite median price bottomed out at $470,017 in January 2009. The composite gradually increased to $509,030 in July, before the nine-month-long run of declines. The May median is 6.1% below last year's July peak. In the 26 markets Altos tracks, listing prices were up during the month of May compared to April in 18 markets. San Francisco experienced the largest increase with listing prices rising 2.4%, followed by Dallas and Washington, DC with increases of 1.4% and 1.2% respectively. Asking prices were down the most in Miami (1.7% decline), and listing prices were also down in Detroit, Las Vegas, Los Angeles, New York, Phoenix, Salt Lake City and San Diego. Home inventory was also on the rise in 22 of 26 markets, month-over-month. The biggest increases of houses on the market were in Boston and San Francisco, up 5.9% and 5.5%, respectively. Altos noted the increase in inventory appears to be largely a seasonal shift. However, the report said it remains to be seen whether demand will hold up after the recent expiration of government incentives or whether inventory will rise sharply over the summer as housing demand falls off. The positive price gain news comes on the heels of a report from Fiserv that showed home prices trended up in more than 40% of metropolitan areas (155 of 384 markets) in Q409, including markets in California, Ohio, Michigan and Washington DC. Write to Austin Kilgore.