Electric field measurements were made by a sailplane inside thunderstorms near Langmuir Laboratory and the Magdelena Mountains in central New Mexico. The continuity of these measurements in-cloud allows us to deduce electric field growth rates in six cases ranging from initial electrification through the production of lightning. The electric field data are combined with radar reflectivity data to estimate charge locations and magnitudes. In each case, the domiant charge was negative, associated with a local reflectivity core, and demonstrated a cellular structure centered at altitudes ranging from 5.5 to 7.3 km mean sea level (~3 to ~15¿C). Three distinct phases characterize the electric field measurements during initial electrification: an early stage of slowly increasing field that largely could be explained by the sailplane motion toward the estimated charges, followed by a rapid exponential growth period, and then a plateau in electric field growth rate (at about 300 V m-1 s-1) after the rapid growth period. These six cases extend earlier studies to further establish the character and magnitude of electric field growth during the early stages of thunderstorm electrification. ¿ American Geophysical Union 1989