Dimethyldioxirane oxidises nitrogen-containing substrates. The sites of oxidation are generally the sp3 nitrogen atoms in the molecules although other reactive groups can be oxidised if present. An indication of the reactivity of different dioxiranes was obtained qualitatively from the polarographic peak reduction potentials and quantitatively by reaction with the model substrate 4-nitro-N,N-dimethylaniline. The polarographic peak potentials were shown to be of a similar order to those of typical acyclic peroxides. The rank order in terms of reactivity was shown to be methyl(trifluoromethyl)dioxirane > dimethyldioxirane > ethylmethyldioxirane. The rate of the reaction was not influenced by pH or ionic strength but was accelerated greatly by the presence of water. An explanation for this observation was proposed through consideration of dielectric constant and hydrogen bonding effects.