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Third-order intermodulation in capacitively coupled microelectromechanical filters is analyzed. Parallel-plate transducers are assumed and, in addition to the capacitive nonlinearities, also the usually much weaker second- and third-order mechanical resonator nonlinearities are taken into account. Closed-form expressions for the output signal-to-interference ratio (SIR) and input intercept point are derived. The analytical results are verified in experiments and in numerical harmonic-balance simulations. It is shown that intermodulation as a function of frequency is asymmetric with respect to the passband. The results are valuable in designing micromechanical filters, for example, for communication applications.