The in vitro degradation of microtubule‐associated protein 2 (MAP‐2) and spectrin by the calcium‐dependent neutral protease calpain was studied. Five major results are reported. First, MAP‐2 isolated from twice‐cycled microtubules (2XMT MAP‐2) was extremely sensitive to calpain‐induced hydrolysis. Even at an enzyme‐to‐substrate ratio (wt/wt) of 1:200, 2XMT MAP‐2 was significantly degraded by calpain. Second, MAP‐2 purified from the total brain heat‐stable fraction (total MAP‐2) was significantly more resistant to calpain‐induced hydrolysis compared with 2XMT MAP‐2. Third, MAP‐2a and MAP‐2b were proteolyzed similarly by calpain, although some relative resistance of MAP‐2b was observed. Fourth, the presence of calmodulin significantly increased the extent of calpain‐induced hydrolysis of the α‐subunit of spectrin. Fifth, the two neuronal isoforms of brain spectrin (240/235 and 240/235E, referred to as α/βN and α/βE, respectively) showed different sensitivities to calpain. αN‐spectrin was significantly more sensitive to calpain‐induced degradation compared to αE‐spectrin. Among other things, these results suggest a role for the calpain‐induced degradation of MAP‐2, as well as spectrin, in such physiological processes as alterations in synaptic efficacy, dendritic remodeling, and in pathological processes associated with neurodegeneration.