Mercury was measured in accumulated snow (March 1982) sampled from around Lake Superior and in rainfall from Duluth, Minnesota (June-September 1982 and March-November 1983), Forbes Township, and Dorset in northwestern and central Ontario, respectively (May-September 1983). Methods of melting snow and collecting rain samples were investigated to avoid loss of mercury during the melting process and sample shipment and storage. Low concentrations in snow and rain required greater analytical sensitivity. A detection limit of 0.008 plus or minus 0.004 micrograms/L of mercury (N = 26) was attained using the cold vapor technique; and by utilizing a gold gauze amalgam accessory for preconcentration, a detection limit of 0.005 plus or minus 0.003 microgram/L (N = 13) was attained. Regional comparisons of mercury accumulation in the snow pack across the northern parts of Minnesota, Wisconsin, Michigan, and Ontario show highest values, 0.10 plus or minus 0.17 micrograms/L Hg, in the Grand Rapids, Minnesota, area and lowest values in remote areas of Minnesota and Ontario. Rainfall concentrations of total mercury were substantially higher than snow accumulation and were mainly of inorganic forms (73%).