The radio signal from the Galileo probe to the orbiter experienced attenuation due to ammonia in Jupiter's atmosphere during the probe descent. A profile of the ammonia content as a function of depth in the atmosphere has been derived from the measurements of the attenuation. The derived ammonia abundance rises to a molar fraction of 700¿100 parts per million for pressures greater than 7 bars, about 4 times that expected based on the solar abundance of nitrogen. ¿ 1998 American Geophysical Union