Three heat flow determinations a were made in M'Clure Strait between Prince Patrick and Banks Islands in the northwestern part of the Arctic Archipelago of Canada. The three stations lie within 55 km of a point some 130 km SSW. of Mould Bay, Prince Patrick Island, and yield a weighted mean heat flow of 0.84 ± 0.09 μcal cm−2 s−1, or 57% only of the worldwide continental average. The measurements were made from sea ice in water depths of some 430 m using a thermal probe and portable equipment carried in a fixed-wing aircraft.Instrumental limitations and errors are discussed, together with environmental factors. The uncertainties in interpreting this result as a truly subnormal equilibrium heat flow are outlined but it is concluded that the calculated systematic errors are unlikely to exceed 25%. Consequently in the absence of any known major perturbing effect, it must be concluded that the structure responsible for the suppression of vertical magnetic held variations at Mould Bay observatory does not extend 130 km to the south, is not produced by an anomalously high near-surface temperature, or is of late-Quaternary origin.