Hundreds of police had barricaded themselves inside the radio and TV station in Kragujevac, about 90 miles south of Belgrade, to prevent their takeover by new city officials, who support the Serbian opposition.
Thousands of opponents to President Slobodan Milosevic surrounded the television station, and were threatening to use force to enter.
About 30 cars and trucks blocked traffic on the main road between Kragujevac and Belgrade yesterday afternoon. But some 60 riot policemen charged with batons, badly beating up two protesters and breaking up the blockade.
Police arrested at least eight opposition activists during road blockades in several cities, as the opposition called for its supporters to block roads across the Serb republic.
Kragujevac was won by opponents of Mr Milosevic in local elections in November. In contrast to his treatment of many other cities and towns in Serbia, Mr Milosevic has allowed the opposition to take power there.
Control of the media is a central issue in the struggle between Mr Milosevic and the opposition. Whoever wins city hall controls local radio and television stations. Mr Milosevic has used a monopoly on the media to keep support, especially in provincial towns and rural areas. He needs to have control of the media message this year as Serbia prepares for presidential and parliamentary elections.