Ezra 2:21-70; Nehemiah 7:26-73a

Both Ezra 2:61-63 and Nehemiah 7:63-65 record the dilemma of some supposed members of priestly families, namely that no family records could be found to prove that they indeed belonged to the lineage of Israel's priests. What happens? They are not permitted to perform priestly duties--not until a priest becomes established who ministers "with the Urim and Thummim." 

Urim and Thummim are sacred lots used by the Hebrews in Ezra's and Nehemiah's era.  I presume that a priest ministering with the Urim and Thummim would be able to get a "yes or no" answer to the question of the families' claim that they belong to Israel's priestly tribe.