An analysis of high-resolution magnetic field measurements from the GSFC (Goddard Space Flight Center) magnetometer on Explorer 43 showed that low magnetic field intensities (<1&ggr;) in the solar wind at 1 AU occur as distinct depressions, or 'holes,' in otherwise nearly average conditions. These magnetic holes are new kinetic scales phenomena, having a characteristic dimension of the order of 20,000 km. They occurred at a rate of 1.5/d in the 18-day interval (March 18 to April 6, 1971) that was considered. Most magnetic holes are characterized by both a depression in [B> and a change in the magnetic field direction, and some of these are possiby the result of magnetic merging. However, in other cases the direction does not change; such holes are not due to merging but might be adiamagnetic effect due to localized plasma inhomogeneities.