Exhaustive measurements of emission line widths from populations of HII regions in external galaxies yield two results which are not easy to explain. Firstly a large fraction of the line widths are supersonic, and although sufficient energy is in principle available from the ionizing stars, it is by no means obvious how this is converted into turbulent energy within the HII regions. Secondly a detailed comparison of HII region masses derived from these line widths assuming viriality
(in those cases where this does appear to hold) overestimates the mass by half an order of magnitude. The presence of turbulent magnetic fields with strengths of order a few tens of microgauss can be invoked to account for these discrepancies. The difficulties of detecting and measuring such fields make the problem a technical challenge of interest for the coming years