Measurement of the mass difference m(B^{0})-m(B^{+})

Using 230 x 10(6) B (B) over bar events recorded with the BABAR detector at the e(+)e(-) storage rings PEP-II, we reconstruct approximately 4100 B-0 -> J/psi K+pi(-) and 9930 B+ -> J/psi K+ decays with J/psi -> mu(+)mu(-) and e(+)e(-). From the measured B-momentum distributions in the e(+)e(-) rest frame, we determine the mass difference m(B-0) - m(B+) = (+0.33 +/- 0.05 +/- 0.03) MeV/c(2).