This study is based on monthly (1998-1999) sampling of domestic landfill leachates situated in Etueffont (Belfort, France). The results show that rain flows and water flows are not correlated. Overall, the measurements carried out monthly on leachates demonstrated a seasonal evolution of some chemical parameters all over the year. During summer, the rise of the ambient temperature resulted in an increase of the overall bacterial activity as shown by the decrease of the BOD (Biological Oxygen Demand), COD (Chemical Oxygen Demand) parameters and a rise of pH (8). Therefore, the BOD/COD ratio which describes the biodegradability of the medium reaches 0.18. Chloride concentrations are high (700 mg. l-1) and concentrations of total nitogen (NT) and ammonia (NNH4+) increase. During winter, the dilution induced by the rain flow points out a reversed pattern. This resulted in a decrease of the chloride concentrations (100 mg. l-1) and that of NT (198 mg. l-1). Consequently, the BOD and the zinc concentrations increase. The variation of zinc concentrations are well correlated with precipitations. This is mainly due to the heterogenous distribution of the zinc in the landfill.