A relativistic calculation of the electron self-energy in a strong hom
ogeneous magnetic field is presented, and the final expressions are ca
lculated numerically for the Landau levels N = 0,1,2,3 and both spin p
rojections (sigma = +/- 1). For a given N > 0 the energy of the spin-u
p state (sigma = + 1) increases monotonically, but the spin-down (a =
- 1) energy is negative for small fields, shows a minimum, and then in
creases for large fields; a crossing of levels appears for N > 0. The
total decay rates for these states are also obtained, as well as the s
pin-flip transition probability for (N = 1, sigma = + 1) --> (N = 1, s
igma = -1). It turns out that this transition rate is extremely small
compared to the usual cyclotron emission rates.