The watershed approach can provide a useful tool for asking questions about patterns and processes that occur at the scale and complexity of entire watersheds. The study of small streams is of special importance in such studies, since the chemistry of small streams often reflects biological, geological and chemical processes that occur within entire watersheds. We here provide a general introduction to the watershed approach, and to comparative studies of small streams. As a case example, we use the watershed approach to ask questions about spatial and temporal variability in sulfur dry deposition in four replicated watersheds. In addition, we will compare data from streams and precipitation between Chiloe National Park, Chile and the Hubbard Brook Experimental Forest (HBEF), USA. These preliminary comparisons suggest that while precipitation and streamwater at the HBEF is dominated by atmospheric pollution inputs, the temperate forests of Chiloe show evidence of exceptionally clean precipitation and streamwater, dominated by inputs of sea salt ions (Ne and Cl-). Streamwater chemistry in Chiloe is low in nutrient levels suggesting highly weathered, nutrient poor soils. These preliminary observations raise important questions about the source of nutrients for the temperate forest at Chiloe, and the ability of the forest to tolerate disturbances such as deforestation