A method for measuring NH3 colorimetrically by Nesslerization without distillation is proposed. Precipitation of CaCO3 is prevented by adding Na salicylate, which chelates the Ca2+, but not the Hg2+ of Nessler's reagent. NO3 - can be measured in the same way after reduction with TiCl3. Precision and accuracy are those of a colorimetric method ; the sensitivity is somewhat lower than with the indophenol-blue method using phenol, but about the same as when using salicylate.