Giant magnetoresistance (GMR) magnetoelectronics has been an area of growing technological and commercial interest. GMR hard disk read heads have enabled a order-of-magnitude increase in storage density. Nonvolatile random access memory (NVRAM) utilizing GMR technology is an area of intense research and prototype devices are being introduced. Still other devices include magnetic field sensors as well as rotation and displacement sensors. A unique application for GMR devices is in the detection of magnetic microbeads commonly used in biological research for cell and biomolecule separation. We are developing a biosensor, the Bead ARray Counter (BARC),@footnote 1@ that uses these microbeads as labels to detect DNA hybridization at specific areas over an array of GMR sensors micro-fabricated on a chip. Eventually, the BARC chip is envisioned to be akin to GMR NVRAM, with millions of sub-micron GMR elements enabling simultaneous detection of thousands of DNA sequences with high sensitivity and dynamic range. We will discuss the special magnetotransport, micromagnetics, and microfabrication issues required for the development of high-density GMR-based biosensor arrays. This work was done in collaboration with P.E. Sheehan, R. L. Edelstein, C. R. Tamanaha, L. Zhong, S. Bonnak, R. J. Colton, L. J. Whitman, and G.A. Prinz. @FootnoteText@@footnote1@Edelstein et al., Biosensors & Bioelectronics 14, 805 (2000).