Magnetic field effects on the triplet sensitization reaction of p-aminophenyl disulfide were studied in a sodium dodecylsulfate micellar solution by a nanosecond laser flash photolysis technique under ultrahigh magnetic fields of up to 28 T. The yield of the escaped p-aminophenyl thiyl radical decreased by 6 +/- 2% at 28 T compared with that at 0 T.