At IBM Research Laboratories in Yorktown Heights, NY, David Awschalom and co-workers are now able to study the magnetic properties of a single particle of magnetic material in the shape of a cylinder only 150 Å in diameter and 300 Å in length. They make use of an integrated DC SQUID microsusceptometer (1988 Appl. Phys. Lett. 53 2108), shown in figure 1, which is capable of detecting the magnetic field produced by the mere one million electron spins contained in the particle. The energy sensitivity of the instrument is very near the quantum limit set by the uncertainty principle, namely h divided by the time interval of observation (this is equal to the inverse frequency bandwidth). This accomplishment represents another great feat in the area of ultra-sensitive detectors and miniature sample preparation.