Abstract‐Large phytochrome immobilized via anti‐phytochrome immunoglobulin bound to Sepharose beads was irradiated to saturation with unpolarized far‐red light. The apparent absorbance level was recorded in a dual wavelength spectrophotometer with both measuring beams set to either 660 or 730 nm and polarized perpendicular to each other. The sample was then irradiated with red polarized light. The apparent change in absorbance obtained after this irradiation indicated that purified phytochrome could show linear dichroism. From the absorbance values obtained it was computed that the direction of the long‐wavelength transition moment changes by either 32 or 148o, when phytochrome is transformed from Prto Pfr. Considering the model of Hahn and Song (1981) the latter value appears more likely. In light of these results, the conclusions drawn fromin vivoexperiments on action dichroism inDryopteris(Etzold, 1965),Adiantum(Kadotaet al.,1982) andMougeoutia(Haupt. 1970), which point to a 90orotation. should be recon