  We present empirically determined ionization conditions for the winds of 106
luminous B0 to B5 stars observed by IUE. The UV wind lines are modelled to
extract products of mass-loss rates (Mdot) times ionization fractions (Mdot
q_i(w), where w = v/v_infty) for N V, C IV, Si IV, Si III, Al III and C II. We
describe the general behaviour of the Mdot q_i(w) and their ratios,
demonstrating that the wind ionization increases with distance from the star,
contrary to recent findings for O star winds. Using empirical mass-loss rates
(from H alpha observations) and model prescriptions, we derive mean q_i(w)
values integrated over the wind, <q_i>. These <q_i> are quite small, never
exceeding 15% for Al III or 2% for Si IV. This is surprising, since the <q_i>
for these ions clearly peak within the observed spectral range. We conclude
that the low <q_i> arise because the <Mdot q_i> are underestimated by the wind
models, which assume that the outflows are smooth when they are, in fact,
highly structured.
