Laser flash photolysis (308 nm) of endo-7-chlorodibenzo[a,c]bicyclo[4.1.0]heptane produces phenanthrene and chlorocarbene, which can be trapped with pyridine to form an ylide. The ylide absorbs strongly at 374 nm, and its lifetime is many tens of microseconds. It was not possible to resolve the grow of the ylide due to the rapid reaction of chlorocarbene with solvent. It was possible, however, to deduce the lifetimes of chlorocarbene in various solvents by measuring the yield of ylide as a function of [pyridine] and assuming that the absolute rate constant of reaction of chlorocarbene is the average of those of dichlorocarbene and alkylchlorocarbenes, which have been previously reported. Absolute rate constants for the reaction of chlorocarbene with alkenes were then deduced by the Stern-Volmer method, and the relative reactivity of chlorocarbene toward alkenes was found to be in good agreement with the relative reactivities of the lithium-chlorocarbene complex or carbenoid determined by analysis of product mixtures reported by Closs and Schwartz.