Pennsylvania held primaries for the Democratic and Republican Parties on May 16. In both the 9th U.S. House district, and the 15th U.S. House district, no Democrat had appeared on the primary ballot. However, in both districts, a Democrat received enough write-in votes to be nominated. Pennsylvania law requires 1,000 signatures for a write-in candidate in a primary to be nominated. The write-in winners are Tony Barr in the 9th district, and Charles Dertinger in the 15th district. Thanks to Tony Roza for this news.

As reported earlier, on May 2, Ohio Democrats also used write-in votes to nominate a candidate for US House this year, in the 6th district.