Microtubules in living cells frequently bend and occasionally break, suggesting that relatively strong forces act on them. Bending implies an increase in microtubule lattice energy, which could in turn affect the kinetics and thermodynamics of microtubule-associated processes such as breaking. Here we show that the rate of microtubule breaking in fibroblast cells increases approximately 40-fold as the elastic energy stored in curved microtubules increases to > approximately 1 kT/tubulin dimer. In addition, the length-normalized breaking rate is sufficiently large (2.3 breaks x mm(-1) x minute(-1)) to infer that breaking is likely a major mechanism by which noncentrosomal microtubules are generated. Together the results suggest a physiologically important, microtubule-based mechanism for mechanochemical information processing in the cell.