It is shown that the fieldB= 22 kG which exists in each Weiss domain even in the absence of an applied field should cause certain anomalies in the residual resistance of very pure polycrystalline iron. The residual resistance in zero applied field is no longer proportional to impurity concentration. It may even have a minimum as a function of impurity concentration. The minimum should correspond to a resistivity ratioR273/R4.2of roughly 300. This explains why the resistivity ratio of samples of zone‐refined polycrystalline iron is usually found to be no higher than 200 or 300. The same internal field is also shown to be the cause of the resistance decrease in a small longitudinal field, observed in very pure iron and nickel at low temperature. A decrease is also expected in a small transverse field if the sample is very slightly misoriented.