This is a brief report on previously unpublished Explorer I observations of the precipitation of energetic particles from the Earth's inner radiation belt during the great geomagnetic storm of February 11, 1958 (maximum negative value of the Sugiura equatorial index Dst=-409&ggr;) and during the lesser storm of March 11--15, 1958 (Dst=-126&ggr;). These first ever satellite observations within the magnetosphere showed that there was a good linear correlation between a simple quantitative measure of particle precipitation and Dst for the February storm but that such a relationship was less well determined by the sparse data for the more complex March storm. In time coincident with the satellite-detected effects there were many other geophysical phenomena including exceptional low-latitude aurorae over the southern United States and Japan during the February storm. Subsequent observations of the precipitation of energetic particles from the inner radiation belt were confined to quiescent or moderately disturbed conditions until about three decades later. Our Explorer I data provide an historical context for contemporary work as solar activity approaches its predicted next maximum in 2000--2001. ¿ 1999 American Geophysical Union