The dissociation of the metal-metal bond in mixed-metal porphyrin dimers was investigated in the picosecond-microsecond time domain by 355 nm flash photolysis. The photogenerated metalloradicals, [(porphyrin)M-.] where M = Rh, In, Tl, undergo transformations with a first-or pseudo-first-order kinetics, k = 4.1 x 10(10) s(-1), into intermediates that can be scavenged with CH2Cl2. On a longer time scale, dependencies of the reaction rate on the photolyte and metalloradical concentrations reveal that the secondary products undergo recombinations among themselves and reactions with excess parent complex. The illustration shows the time-resolved spectra recorded in 355 nm flash irradiations of (TPP)Rh-In(OEP) in toluene.