(CNN) - Sen. Scott Brown of Massachusetts raised $5 million in the second quarter of the year, his campaign said Wednesday, which is approximately $3 million less than his Democratic challenger's haul.
His campaign ended the three-month period including April, May, and June with $15.5 million cash on hand and did not say the committee held any debt.
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Although Democrat Elizabeth Warren raised $8.6 million in the quarter, she has $13.5 million cash on hand, her campaign said on Monday.
Brown is a first-term Republican who won his seat in a January 2010 election to replace the late Sen. Ted Kennedy.
The Democratic nominee is Elizabeth Warren, a Harvard law professor who previously headed a federal consumer protection agency.
Each campaign has challenged that the other is benefiting disproportionately from out-of-state donors.
Brown's effort said 66% of donations to the incumbent's campaign came from within Massachusetts.
Neither Brown nor Warren have filed their official reports with the Federal Election Commission, which are due by July 15.
– CNN's Ashley Killough and Gregory Wallace contributed to this report