The anomalous stress peak has been examined in Fe-40%Al single crystals compressed along a direction near [001]. A sharp stress peak is observed at 525 °C with anomalous strengthening found only about 25 °C on each side of the sharp peak. Deformation by 〈 111 〉 superdislocations at low temperatures is made more difficult near the stress peak as the dislocations react to produce short, essentially immobile 〈 100 〉 segments and as edge superdislocations decompose to 〈 100 〉 and 〈 110 〉 dislocations, poorly mobile at such temperatures. There is no evidence of superdislocation pinning by extensive cross-slip, by climb, or by interaction with vacancy loops. At temperatures immediately above the stress peak 〈 110 〉 and 〈 100 〉 dislocations move, while at higher temperatures 〈 100 〉 dislocations alone ensure deformation. The flow stress falls because of the thermal activation of glide and because of the limited possibilities for dislocation pinning through intersections and reactions as deformation occurs by 〈 100 〉 dislocations alone. Many processes have been observed in the temperature range encompassing the stress peak and deducing the critical mechanisms is difficult. The role of the orientation of the applied stress in determining the relative rate of dislocation interactions and glide is emphasized.