The distribution of sea ice meltwater and meteoric water in the eastern Canadian Arctic has been studied by oxygen isotope techniques. The distribution pattern of sea ice meltwater is presented. A comparison of the relative amounts of sea ice meltwater and meteoric water in the surface layer shows that more than 25% of all the samples with sea ice input contained more sea ice input than meteoric input. Sea ice meltwater/meteoric water ratios as high as 4.7 have been observed. The depth of sea ice meltwater penetration varies from 50 m in Baffin Bay to 140 m in Lancaster Sound. Calculated sea ice thicknesses range from 0.5 to 4.5 m with a mean of 1.5 m, in good agreement with ice core data. The significance of sea ice meltwater for chemical, physical, and biological oceanography is briefly discussed. The principles and limitations of using oxygen isotopes to detect brines are discussed in the Baffin Bay setting. The isotopic compositions of possible source waters for Baffin Bay bottom water are examined.