Abstract During the period June 1978–May 1980, a network of about 20 wet-only, monthly deposition monitors was operated within a 150 km radius of Sudbury, Ontario, the location of the INCO and Falconbridge Ni smelters, to examine the long term wet deposition pattern in the Sudbury Basin. During most of the first study year (June 1978–May 1979), the INCO smelter (the larger of the two sources) was not operating, and therefore the data were grouped into two periods June 1978–May 1979, and June 1979–May 1980 to look for any smelter impact. Geometric means of the 78/79 and 79/80 pH and concentration measurements of all network stations were: pH, 4.1 (78/79)and 4.2 (79/80); and in mg (1175-1)fx−1, SO42− 3.4 and 3.4; N-NO3−, 0.6 and 0.6; N-NH4+, 0.3 and 0.4; Fe, 0.06 and 0.07; Cu, 0.003 and 0.004; Ni, 0.001 and 0.002; Pb. 0.013 and 0.009; Zn, 0.011 and 0.009; Cr, 0.0004 and 0.0004, and Cd, 0.0007 and 0.0005. Results of the Student t- test indicate that there was no statistically significant differences in the two years' concentrations. The precipitation concentration and wet deposition fields for the June 1978 to May 1979, and June 1979 to May 1980 periods were compared. Contrary to expectations, there was no readily observable difference on the local precipitation acidity. The greatest impact of smelting activities near the source was found to be for Cu and Ni. Pb and Cd showed only a small smelter impact. Results for the other substances examined (e.g. SO42−, NO3− NH4+ and Fe) apparently were largely governed by non-smelter-related phenomena, such as long-range transport into the study area, and contributions of local wind-blown dust or vehicular traffic.