A review of the current status of the detection of strong non-intrinsic variability in the CLASS gravitational B1600+434 will be given, focusing on 1998 VLA 8.5-GHz and 1998/9 WSRT multi-frequency observations. I will show that this variability can best be explained in terms of radio-microlensing. I then proceed to show new results from a 1999/2000 multi-frequency VLA monitoring program, in particular the detection of a strong non-intrisic event in the 8.5 and 5-GHz light curves of the lensed image that passes predominantly through the dark-matter halo of the lens galaxy. We interpret this event, which lasted for several weeks and had a maximum amplitude of about 30%, as a radio-microlensing caustic crossing, i.e. the superluminal motion of a microarsec-scale jet component in the lensed source over a single caustic in the magnification pattern, which has been created by massive compact objects along the line-of-sight to the lensed image. Finally, I will discuss both the implications of this work and several new programs with the VLA, MERLIN and WSRT that will investigate radio-microlensing in more detail in the near future.