The intensity level of ultrasonic ambient noise, and its spectral distribution up to 30 kc.,have been measured in the jungles of Panama, during the rainy season, for all times of the day, at many representative locations. Contrary to popular supposition, the jungle ordinarily is not extremely noisy either in the audible or ultrasonic range. The ultrasonic intensity seems to be caused largely by the high frequency components of the more strident insect noises which usually are still more intense in the audible region.