Formyl chloride has been generated in aqueous solution (i) by stopped-flow ozonation of vinyl chloride and (ii) by reacting dichloromethyl radicals with OH radicals using the pulse radiolysis technique. Vinyl chloride reacts in water with ozone (k=1.7x10(4) dm(3) mol(-1) s(-1), as determined by stopped-flow) yielding as final products (mel per mol of ozone) chloride ions (1.05), CO (1.01), and formate ions (0.06). Hydroxymethyl hydroperoxide (formaldehyde plus H2O2; 1.08) is also formed. HCl and formic acid are formed in less than 2 ms (the detection limit of the stopped-flow setup). At high pH the CO yield decreases (at pH 13.6 by 50%). It is concluded that the precursor of CO, HCl, and formic acid is formyl chloride. It predominantly decays into CO and HCl, and only at very high pH can hydrolysis to formic acid and HCl compete successfully. Using the pulse radiolysis technique dichloromethyl radicals are generated in Ar-saturated solutions from chloroform by reacting it with the solvated electron (originating from the radiolysis of water). The OH radicals (also from the radiolysis of water) partially react with the dichloromethyl radicals yielding dichloromethanol. Alternatively, dichloromethanol is generated in N2O-saturated solutions from dichloromethane, where some of the OH radicals are allowed to abstract an H atom from dichloromethane and another fraction to add to the dichloromethyl radicals. The observed conductivity changes are attributed to a very rapid decay (t(1/2)<20 mu s) of dichloromethanol into formyl chloride and HCl followed by the decay of formyl chloride into CO and HCl (k=10(4) s(-1)). From these data and the decrease of the CO yield at high pH (ozonation of vinyl chloride) it is estimated that the OH--induced hydrolysis of formyl chloride occurs with a rate constant of ca. 2.5x10(4) dm(3) mol(-1) s(-1).