The recombination of pairs of para-substituted phenylthiyl radicals inside micellar supercages was studied by means of a nanosecond laser flash photolysis technique. Singlet and triplet pairs were formed by direct excitation and by triplet-sensitized photolysis of the corresponding disulfides, respectively. Magnetic field effects (MFEs) on the yield of escaped thiyl radicals were found for the triplet-sensitized photolysis of the p-amino compound. For the p-hydroxy-, p-methoxy-, and p-butoxy compounds, short-lived MFEs were observed but it is unlikely that they arise from the recombination of the thiyl radicals. No MFE was found on pairs of p-chloro-substituted and unsubstituted phenylthiyl radicals within experimental error. The absence of MFE is in this case explained by large spin-orbit coupling caused by orbital degeneracy. A stabilization mechanism of the (p-aminophenyl)-thiyl radicals lifts that degeneracy and reduces spin-orbit coupling. Variations of the MFE over the absorption spectrum were used to assign the MFEs to certain species in the reaction systems.