On August 15, 1984, we made balloon measurements of the electric field and of the charge and vertical velocity of precipitation particles in a thunderstorm over Langmuir Laboratory. Substantial quantities of positively charged precipitation, comprising a lower positive charge center, were collected before the storm's first lightning flash. Possible origins of the positive charge are discussed. Negatively charged precipitation and positively charged cloud particles found higher in the cloud seem to have generated electrical energy in the way suggested in the typical precipitation theory of thunderstorm electrification. ¿ American Geophysical Union 1993