The decomposition of 9-diazofluorene (FIN₂) brought about at a platinum anode or by chemical oxidants, Cu(BF₄)₂ or (p-BrC₆H₄)₃N⁺˙SbCl₆^–, in CH₃CN solution leads to formation of mixtures of bifluorenylidene and fluorenone azine in high yield. The reactions have been studied kinetically by conventional means and using the transient electrochemical techniques derivative linear sweep voltammetry (I.s.v.) and derivative cyclic voltammetry (d.c.v.). Constant-current electrolysis of FIN₂ shows the characteristics of a chain process. The chemical oxidants give rise to a rate law –d[FIN₂]/dtk[FIN₂][oxidant] above a critical oxidant level, and the value of k is the same for both oxidants, even though their oxidation potentials are substantially different. It is inferred that the process studied is the chain propagation step in which the chain carrier reacts with a molecule of FIN₂. Under the conditions of I.s.v. and d.c.v. experiments, it is shown that the instantaneously formed FIN₂⁺˙ is consumed in a rapid process which is second order with respect to the cation radical and has a rate constant of 1.9 × 10⁸ l mol ^–1 s^–1; it is suggested that this process is cation radical dimerisation. Since the product of this step rapidly yields bifluorenylidene, it is argued that the slower macroscopic chain reaction do not involve dimerisation, but rather that FIN₂⁺˙ rapidly attacks a further FIN₂ molecule to generate the chain carrier which must have a lower oxidation potential than FIN₂⁺˙. Possible structures for the chain carrier are considered in the light of earlier e.s.r. evidence for a radical intermediate.