A joint study of strain, anisotropy of magnetic susceptibility (AMS), and paleomagnetism has been conducted in the deformed red beds of the Ordovician Pont-R¿an formation, Brittany, France. Analysis of results from 13 sampling sites shows that homogeneous strain, estimated from the shape of elliptical reduction spots in each site, controls the development of a magnetic fabric during the Hercynian folding of this formation. The good correlation between strain and AMS tensors is interpreted as mainly arising from a strain-induced progressive rotation of planar hematite that tends to align within cleavage plane. This rotation of magnetic carriers in turn induces a rotation of net measurable pretectonic remanent magnetization toward cleavage. Because of the high angle between the initially subvertical Ordovician remanent magnetization and the regionally subhorizontal shortening direction, this deviation of the pretectonic magnetization is achieved without any scattering but with a probable clustering effect upon within-site initial dispersions. For the same reason the overall distribution of mean-site pretectonic magnetization vectors is clustered at the in situ deformed state. This results in an anomalous behavior of the classical fold test, that could erroneously lead to assignment of a syntectonic to post tectonic age to the magnetizations. Finally the strain removal technique based upon the passive behavior hypothesis is applied to the deviated vectors. It allows recovery of the initial direction of these pretectonic Ordovician magnetizations (D=235¿, I=75¿, α95=6.5¿). ¿ American Geophysical Union 1988