The explosives in the ammunition used by the Swedish Armed Forces today do not meet contemporary environmental demands concerning toxicity and biological degradibility. Currently a great deal of research is done to replace these out-of-date environmental hazardous explosives by less hazardous. One of the aims in the research project "Methods for Environmental Risk Assessment (Metoder för miljöriskbedömning) is to characterise the expose related and effect related properties of new explosives. Two new explosives, ADN (ammonium dinitroamide) and FOX-12 (guanylurea dinitroamide) have been developed at the Department of Energetic Materials, FOA 21. The aim of this work was to examine the acute toxicity of these two explosives in the water flea, Daphnia magna. The calculated acute toxicity (EC50) value of ADN in the water flea, D. magna, was 405 mg/l after 48 hours exposure. With reference to the concentration of ammonium in the water ADN is equally acute toxic to D. magna as ammonium chloride. Animals exposed to ADN were sedated (moving very slow in the water) compared to unexposed animals. The solubility of FOX-12 in water is limited. A saturated solution of FOX-12 was not acute toxic to the water flea. Future work will focus on the investigation of the effects of these substances on other species and the long time effects on water flea.