We describe a low-noise scanning Hall probe microscope having unprecedented magnetic field sensitivity (similar to 2.9x10(-8) T/root Hz at 77 K), high spatial resolution, (similar to 0.85 mu m),nd operating in real-time (similar to 1 frame/s) for studying flux profiles at surfaces. A submicron Hall probe manufactured in a GaAs/A1GaAs two-dimensional electron gas (2DEG) is scanned over the sample to measure the surface magnetic fields using conventional scanning tunneling microscopy positioning techniques. Flux penetration into a high T-c YBa2Cu3O7-delta thin film has been observed in real time at 85 K with single vortex resolution. Flux is seen to enter the film in the form of vortex bundles as well as single flux quanta, Phi(0). (C) 1996 American Institute of Physics.