A reliable leadfield matrix is needed to solve the magnetoencephalography/electroencephalography (M/EEG) source localization problem. The computation of this matrix requires sev- eral physical parameters, including the conductivity of the tissues that compose the subject’s head. Since it is not precisely known, we modify a recent Bayesian algorithm to estimate the skull conductivity jointly with the brain activity directly from the M/EEG measurements. Synthetic and real data are used to compare our technique with two optimization algorithms, showing that the pro- posed method is able to provide results of similar or better quality with the advantage of being applicable in a more general case.