The objective of the proposed research is to continue to develop ultra-high resolution, Superconducting Quantum Interference Device (SQUID) magnetometers (UHRSM) that are optimized for the imaging of the magnetic fields produced by action currents, remanent magnetization, and magnetic susceptibility in isolated living tissue and small experimental animal preparations at the scale of 100 m. Such measurements are not yet in wide spread use, primarily because of the limitations and costs of existing instrumentation. This project is designed specifically to address these points. The proposed instruments will be capable of making measurements that are impossible with any other technique, and should lead to new insights into cellular biology, electrophysiology, botany, embryology, magnetoreception, immunodiagnostics, and neurophysiology.