An automatic procedure for the determination of ammonia in sea water is described. The method is based on the formation ofindophenol blue in presence of a catalyst according to a method developed by KOROLEFF. Dichloro-s-triacine 2, 4, 6 trione is used as stable chlorine donator. Precipitation of magnesium hydroxide in that system is avoided by means of a complexing buffer system. The slight interference of some amino acids caused by the unavoidable heating of the sample stream is studied. The relative standard deviation is 5% between 0 and 10 μg at NH3 - N/l.