The distribution of nitrate and nitrite in two Delaware salt marshes was studied from July 1966 through December 1967. Canary Creek Marsh, located near the mouth of Delaware Bay, was characterized by high salinity, low nitrate water. The Murderkill Marsh, in central Delaware, was characterized by low salinity, high nitrate water. Man-made control structures in the Murderkill Marsh inhibited free tidal exchange and modified the distribution of nitrate and nitrite. Maximum nitrate concentrations occurred in the winter, while minimum concentrations were observed during the summer. Summer nitrate concentrations in the Canary Creek Marsh ranged from undetectable (<2 μg-at/1) to 8 μg-at/1. Winter values were generally between 10 and 25 μg-at/1. At the Murderkill Marsh winter nitrate concentrations ranged from 40 to 100 μg-at/1, and the summer concentrations were generally in the range of 5 to 20 μg-at/1. Nitrite concentrations in both areas rarely exceeded 1.5 μg-at/1, and exhibited no discernable seasonable pattern.