An instrumented free balloon measured electric fields and field changes as it rose through a thudercloud above Langmuir Laboratory, New Mexico. The variation of the electric field with altitude implied that the cloud contained negative space charge of density -0.6 to -4 nCm-3 between 5.5 and 8.0 km MSL. The environmental temperature at these levels ranged from -5¿ to -20¿ C. Our measurements imply that the areal extent of this negative charge center was significantly greater than that of the cloud's intense precipitation shafts. At altitudes greater than 8 km, the instrument ascended past net positive charge. We also inferred from our measurements positive space charge adjacent to the earth's surface (concentration 0.6 nC m-3) and in the lowest portion of the cloud (1.0nC m-3). Electric field changes from intracloud lightning were interpreted by using a simple model for the developing streamer of the initial phase. Thunder source reconstructions provided estimates for the orientation of lightning channels. Seven ''streamers'' so analyzed propagated on the average at 5¿104 m s-1 and carried a current of 390 A. The mean charge dissipated during a flash was 30 C.