The linear and nonlinear response of Fabry-Perot etalons containing a polymer microcrystal solution was studied using the pump-probe technique with a white-light continuum probe. The response was studied at wavelengths away from resonance (700-800 nm) when a near-resonant subpicosecond pump pulse (at 640 nm) was used. A theoretical model used to describe the F-P linear transmission is presented. A blue-shift of the F-P peaks induced by the pump-pulse was clearly observed in all the etalons studied, and the magnitude of the shifts is used to quantify the nonlinear response. The potential of these devices for all-optical switching applications is assessed through the figures of merit W and T, and the recovery time of the nonlinearity. Refractive index changes as large as 1.2 × 10-2 were measured and switching energies as low as 0.9 pJ were calculated at the F-P peaks. The nonlinear response was shown to have an ultrafast recovery, of around 2 ps.