Being quantitatively equal the two independent analytical manners of proceeding, viz. distillation in vacuo and microdiffusion after the Conwayprinciple, are recommended for the estimation of different forms of volatile N and urea N. The two methods fill each other out, the distillation in vacuo being a typical rapid method while estimations performed in Conway units are well fit for mass analyses. Sera made at pH= 5,2 either by means of hydrochloric acid or by colloidal iron were used during these investigations. Analytical data showing the content of total volatile N, trimethylamine N and urea N in fresh and stored fish, also in the salted, smoked and frozen state, are given