Clinton, who is President-elect Barack Obama's choice for secretary of state, said Tehran could improve relations with the United States by offering information on Robert Levinson.
Levinson was last seen on March 8, 2007, during a trip to Kish Island, off the southern coast of Iran. According to his family, he had gone to Iran to seek information on cigarette smuggling.
The United States has called on Iran to cooperate on the Levinson case.
Iranian authorities have said they have no information on his fate.
Christine Levinson, his wife, said in a statement e-mailed to RFE/RL on January 13 that she appreciates Nelson and Clinton discussing her husband's case. She said she hopes the Iranian government will show the “compassion and respect it says it has for all people" and help bring Levinson back to his family.
(by RFE/RL correspondent Golnaz Esfandiari)