Fine fuel moisture content, relative humidity, air temperature, and fire behavior were observed hourly for 48 hours on the North Fork Fire in Yellowstone National Park from August 25 to August 27, 1988. Fine fuel reached minimum moisture content of 3 to 5 percent late in the afternoon, remained below 8 percent until after midnight, then rose to a maximum of 10 to 11 percent around 9 a m. At this time, fires were burning actively well into the night, subsiding to low-intensity surface and ground fire during the morning, then entering the crowns in late afternoon. Live foliage moisture contents were sampled predawn and late afternoon. Standing dead boles, duff, and mineral soil were also sampled. Moisture contents were determined by Camputrac moisture analyzer, ovendrying, and Delmhorst wood moisture meter. Measured fine fuel moisture contents were compared with those predicted by fire behavior analysts' tables and the BEHAVE fire prediction system.