Nitrogen (N) application to corn has been proven to increase yields, but concerns about nitrate-N in ground and surface water led to investigation of this topic. The objective of this experiment is to compare corn grain response to controlled-release urea (ESN) and conventional urea. An ongoing field study is being conducted at two locations in Iowa and yield data will be reported from 2003-2005, measuring corn grain yields. Spring applied N treatments were hand broadcast in 34 kg N ha-1 increments from 0 kg N ha-1 to 202 kg N ha-1, then incorporated into the soil using standard tillage practices for the area. Grain yield increased with N rate at all locations every year. There were significant differences due to N material at four of five site-years. On average, grain yields were 11.1 Mg ha-1 for the ESN and 10.7 Mg ha -1 for the conventional urea.