Misfit dislocations in strained GaAs/(In,Ga)As heterostructures have been studied by high-resolution optical beam induced current (OBIC) imaging. A decrease of the OBIC signal is observed when the focused laser beam crosses a dislocation line. The OBIC contrast is calculated by solving the diffusion equation in a two-dimensional system perpendicular to the misfit dislocation lines. It is shown that the calculated OBIC contrast is in qualitative agreement with the experimental signal when it is assumed that a local increase of recombination rate is present around the dislocation lines.