A new VLF phenomenon named a proton whistler has been identified in the VLF data from Alouette 1 and Injun 3 satellites. Two independent analyses on 12% of the proton whistler Injun 3 data were conducted: a semimonthly sample of data for Injun 3's 10‐month lifetime to determine the gross features of proton whistlers; and a local nighttime and local daytime study of proton whistlers. Six assertions are made from these experimental observations: (1) Proton whistlers are observed only after the reception of an upward‐propagating electron whistler. (2) At a frequency termed the crossover frequency (ω12), the initial electron whistler frequency‐time trace and the proton whistler trace are coincident in time. (3) Proton whistler traces show initially a rapid rise in frequency which starts at ω12and which asymptotically approaches the proton gyrofrequency Ω1(200–650 cps for altitudes of 2700–400 km). (4) Proton whistlers occur more frequently during local nighttime than during local daytime, and they have not been observed to occur below 442 km during local nighttime or below 640 km during local daytime. (5) The ratio of the crossover frequency to the proton gyrofrequency increases with decreasing altitude and approaches unity at an altitude of approximately 440 km around local midnight and approximately 640 km around local noon. (6) There is an apparent northern hemisphere‐southern hemisphere asymmetry in the occurrence of proton whistlers; they occur 3 times more frequently in the northern than in the southern hemisphere. Also, there is a high‐latitude boundary in the occurrence of proton whistlers that seems to correspond with the auroral zone. The theory describing proton whistlers due to Gurne