Embryonic mortality in many aquatic animals, including most amphibian species, is usually very high. In addition to mechanical and chemical defences, some species have developed behavioural patterns that can increase egg survival. For example, females of some newt species protect their eggs by wrapping them in leaves of aquatic plants. We have studied the effects of ammonium nitrate (nominal concentration of 90.3 mg N-NO(3)NH(4)/L) and water acidification (pH 4-5) on egg wrapping behaviour of the dwarf newt, Triturus pygmaeus, and on whether this specific behaviour may protect embryos from contamination. Although either ammonium nitrate or low pH did not inhibit oviposition, the mean percentage of eggs that were wrapped by the females was significantly lower at low pH than in controls. In order to assess the potential effects of oviposition behaviour on embryonic survival, we exposed simultaneously wrapped and unwrapped eggs to ammonium nitrate and acid pH during their development. After 25 days of exposure, ammonium nitrate reduced length and developmental stage at eclosion of the exposed individuals, regardless of whether they were wrapped or unwrapped. The fertilizer caused a significantly higher mortality in unwrapped than wrapped eggs. The potential impact of water pollution on amphibians in the field may include not only direct effects on embryonic and larval survival but also alteration of breeding behaviours, which may reduce reproductive success and ultimately affect population's condition.