The kinetics of addition of tetrafluorohydrazine to olefins in the gas phase which yields vicinal bisdifluoroamines, can be described in terms of the mechanism: NF2+ Of = NF2Of*(1); NF2Of*= NF2+ Of (2); NF2Of*+ Mol = NF2Of + Mol (3); NF2Of = NF2+ Of (4); NF2Of + NF2= Of(NF2)2(5); where Of is an olefin, NF2Of* is an activated radical, and Mol is an inert molecule. Values of k1, k2/k3, and k4/k5 have been found between 41 and 155°, and the Arrhenius parameters calculated for ethylene, but-1-ene, isobutene, 2-methylbut-2-ene, 2,3-dimethylbut-2-ene, and cyclopentane. The results from a very regular pattern of chemical behaviour when taken in conjunction with earlier results for propene and the but-2-enes. The strength of an alkyl–NF2 bond is close to 56 kcal. mole–1.