Studies are presented showing the electrical properties of the highly ionized, detonation‐generated plasmas ejected into various gaseous media at the bare surfaces of high explosives. Theseexternalplasmas are shown to originate from chemionization in the reactions of high explosive at free surfaces and are not produced by thermal ionization in the shock wave propagated in the surrounding gaseous medium. The initial external‐plasma lengthLp* was found to be directly proportional to the lengtha0of the reaction zone of the high explosive‐generating source. Conduction measurements in plasmas propagating in chlorine, oxygen, argon, nitrogen, helium, and air showed that the electron affinity of the gaseous medium is important in determining the rate of decay of the plasma and its ultimate disintegration. The lifetime of external plasmas are substantial in media of low electron affinity, exceeding appreciably 250 &mgr;sec in such media as argon, helium, and nitrogen. Free electrons contribute practically the entire conductivity of these plasmas. Interesting pulsations occur when the external plasmas are generated by a charge of diameter smaller than the constraining tube and upon passing from a smaller into a larger constraining tube. A striking confirmation of the quasi‐lattice or metallic‐like model of plasmas is the observation that the plasma finally ``explodes'' into a gas cloud many times larger when its ion density decays to a critical low level.