Measurements of steam bubble velocities and voidage have been made in the relatively small Core B of the Lingen boiling water reactor. The results of axial scanning in one radial position have produced experimental values of slip ratio, power (from a traveling in-core probe), voidage, and coolant mean density over the core height for this position. This one set of distributions has enabled us to test current U.K. Atomic Energy Authority (UKAEA) models of subcooled boiling and slip ratio against experiment. From the comparisons, it appears that we can predict the onset of voiding well. Of four slip options tested, the current one used by UKAEA computer codes HAMBO and JOSHUA (Bankoff-Jones) predicts too high a slip ratio. A closer fit to experiment comes from the new Bryce flow-dependent slip option. Any changes in the modeling must be checked, however, with coupled thermal-hydraulics/neutronics computations.