Abstract: The baryon octet and decuplet mass spectrum is calculated within the chiral bag model. To zeroth order, this reduces to the MIT bag model. To the next order, baryon self-energies coming from coupling to pions enter. These are about as important as terms from gluon exchange; their inclusion decreases somewhat the colour coupling constant α s needed to fit the empirical baryon splittings. We show that mass splittings resulting from our calculation obey well the Gell-Mann-Okubo mass formulae, although certain terms included would individually violate them. Also the absolute value of the Λ magnetic moment comes out very well. In our theory, part of the mass splitting is a manifestation of the spontaneous breaking of chiral symmetry in the region outside the bag, resulting from the Goldstone pion which is introduced to conserve the axial current at the bag boundary. With inclusion of pionic interactions, the phenomenological zero-point energy introduced through the constant Z 0 in the MIT work is much smaller in order to fit the empirical masses, the pionic self-energies replacing most of it.