The purpose of this study was to understand the differences in tolerance to ammonium nitrate in four Iberian amphibians. Results showed a negative effect on amphibian survival and larvae total length. Three different tolerance groups on amphibian survival were established. The two first groups showed a higher reduction, around 90% and between 70 and 80% after 96 h exposition at the maximum concentration tested (180 mg NH₄NO₃/L), while the third group showed no mortality in any concentration tested. In addition, a reduction in larvae total length was also detected for all four species, with Bufo bufo as the most sensitive species.