1.  Introduction

2.  Ionization rates from different models

   2.1  HII regions with stellar spectral classifications

3.  A larger sample of HII regions

   3.1  H-alpha ionization rates
   3.2  Estimating stellar Q^0 from photometric data
   3.3  Uncertainties
   3.4  Observed vs. predicted ionization rates

4.  Discussion and conclusion