Iran elections: Reformists seek majority in run-off vote
Iranians are voting in the second round of elections which will decide the balance of power between moderates and conservatives in parliament.
In February's first round, reformists made substantial gains but need to win 40 more seats to control the 290-member parliament.
Friday's elections take place in 68 constituencies where no candidate won the minimum 25% of the vote.
Polls are open until 13:30 GMT and results are expected on Sunday.
February's vote was the first since Iran signed a nuclear deal with world powers and was seen as a key test for reformist President Hassan Rouhani.
Moderate allies of Mr Rouhani won 106 seats with a landslide victory in the capital, Tehran.
The results in Tehran were significant because lawmakers from the capital usually determine the political direction of the house, analysts say.
Reformists also made gains in elections for the Assembly of Experts, which appoints the country's most powerful official, the Supreme Leader.
Moderates, however, did less well in constituencies outside the capital, which is where Friday's voting is taking place.
Correspondents say that although the parliamentary elections are not expected to herald large-scale changes in Iranian policies, they could help President Rouhani push through economic and social reforms.