Nationalists in Budapest marked the anniversary of Hungary's 1848 revolution, with most involved in purely peaceful protests.
The main target was Prime Minister Ferenc Gyurcsany, under attack since admitting he lied about the country's finances.
At official celebrations, protesters threw missiles at government politicians.
Separate from the main demonstration, far-right groups welcomed British historian David Irving, recently jailed in Austria for Holocaust denial.
Later, crowds grew following the arrest of right-wing politician Gyorgy Budahazy.
Police considered the evening protest illegal, and moved in to break it up.
Barricades were set up to obstruct the police.
Some threw bottles and stones, and set fire to overturned rubbish bins.
Police responded with water cannon as they attempted to clear the city centre.