In a method for monitoring the load on rotor blades of wind energy installations by measuring acceleration on at least one rotor blade of a wind energy installation and determining load on the rotor blade from the picked-up acceleration signals, dynamic, even uncritical load states can be detected, in differentiated fashion, and combined in a suitable form for evaluation in order to influence, if possible prior to the onset of damage to the rotor blade, the mode of operation of the wind energy installation, in particular the design of the pitch control or angle setting of stall-regulated rotor blades, on the basis both of all of the rotor blades together and of a single rotor blade. Frequency of occurrence of the load values over a certain period of time is determined from amplitudes of the acceleration signal or amplitudes of selected natural oscillations of the frequency spectra are obtained by Fourier transformation.