Hundreds of protesters took to the streets from the early morning -- marching around several blocks and eventually blocking Montgomery Street for several hours.
Among their targets for the day of action were some of the city's biggest financial institutions: the Federal Reserve, Fannie Mae, Wells Fargo, Bank of America, the SEC, Citibank, Chase, and Bechtel, the giant conglomerate.
Some demonstrators chained themselves to the front doors of Wells Fargo corporate headquarters and the Bank of America building.
"The banks are not being responsible and we are tired of being foreclosed, getting in so much debt; it's just time to change the system," protester Wendy Kaufmyn said.
The situation got tense when an officer at that Bank of America protest asked for aid. Dozens of officers arrived and pushed the protesters away. About 18 demonstrators were arrested for blocking the bank building entrances.
A brother and sister from the East Bay sat in front of a Wells Fargo bank, complaining their parents, who live in Chicago, lost their home.
"After 25 years, times were tough and they couldn't make the monthly payments; it's a story that's affecting more and more people and they are losing homes," Max Alpert said.
Wells Fargo issued a statement saying, "In the past year, less than 2 percent of homeowner-occupied loans in our servicing portfolio have proceeded to foreclosure sale."
Bank of America did not comment on the protests.
At another protest in front of the San Francisco Federal Reserve building, a group called "Iraq Veterans Against the War" attracted attention by staging some dramatic scenes. The small but vocal group of veterans came to oppose the very wars they served in in Iraq and Afghanistan.
They said the demonstration also symbolized the way American civil liberties are being eroded at home, in their opinion. They said they chose the Federal Reserve building because it is one of the organizations in the pipeline that is helping fund the war.
Among the protesters was Scott Olsen, the Iraq War veteran who was injured last October when Occupy Oakland demonstrators clashed with police. He says he came out to stand with his fellow veterans against a new law they say gives the president more power to detain American citizens as terrorists.
Friday evening, a group of protesters moved towards Van Ness and occupied the former Cathedral Hill Hotel for several hours. They unfurled a sign from the roof of the building. Police entered the building after them but most of the protesters left voluntarily and only a few arrests were made.
Lyanne Melendez, Jonathan Bloom and Sergio Quintana contributed to this report.