Stable isotopic and chemical evidence has been used to trace sources of sulfate in precipitation in eastern Canada and to apportion this sulfate between natural and anthropogenic origins. A site in Nepean, Ontario was chosen to characterize continental inputs from long-range transport, while two coastal sites in Newfoundland (St. John's and Seal Cove) were chosen to represent the boundary between the marine and continental environments. Precipitation sulfate at the coastal sites should reflect mixing of these two source areas, modified by contributions from local anthropogenic sources. The results of this study show that a three end-member isotopic mixing model using Δ18O and Δ34S describes the composition of sulfate at the Newfoundland sites. The three end-members are (1) sea spray (Δ34S=+21?; Δ18O=+9.5?), (2) long-range transported secondary (anthropogenic) sulfate (Δ34S~+4?; Δ18O~15?), and (3) local primary (anthropogenic) sulfate (Δ34S~+4?; Δ18O=+42?). Mass balance calculations show that as much as 63% of the sulfate deposited at the St. John's site and 18% at Seal Cove is primary sulfate emitted from local pollution sources. Up to 30% of the sulfur deposited in rain at the Newfoundland sites is of continental origin. ¿ 2000 American Geophysical Union