Germplasm resources are the breeding materials used in corn breeding. Recurrent selection methods are used for the genetic improvement of genetically broad-based populations, and similar methods are used to develop recycled inbred lines from elite line by elite crosses. The Iowa program emphasizes genetic enhancement via recurrent selection methods of genetically broad-based synthetic varieties. To determine if the recurrent selection methods are effective in the synthetic populations, lines intermated to form the next cycle population for continued selection also are evaluated in testcrosses and single crosses. The lines that have productive, consistent performance across locations and years are released for possible use by public and private corn breeders.