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The latitudinal distribution of fallout 137Cs in Canada has been determined along a transect extending from 50° to 82° N in 1980. The 137Cs content of lichens, bryophytes, and cushionlike vascular species was measured at 16 sites between Brandon, Manitoba, and Alert, Ellesmere Island. Lichen species were shown to be the most effective biological monitors of 137Cs deposition because of their specific morphology, longevity, and slow growth rates. Dry, exposed ridges were the sites of the highest 137Cs retention by plants. 137Cs levels in vegetation followed a bell-shaped distribution along the transect and the maximum accumulation was measured in samples collected between 60° and 70° N (10 nCi m−2 at 63° N) (1 Ci = 37 GBq). This distribution is the combined result of the original latitudinal deposition of 137Cs, the expired portion of its physical half-life, and the efficiency of biotic and abiotic removal processes along the studied corridor. It is suggested that the long-term implications of 137Cs in the northern food chain ought to be followed and studied more closely in the light of the data presented.