We characterized epinephrine-oxidizing activity in calf thymus nucleosome. The activity was detected in the nucleosome fraction extractable with 10 mM acetate buffer (pH 7.0) and the fraction insoluble in the buffer. Both activities were extremely unstable in the buffer, but stabilized by the addition of MgCI, or CaCI,. The activity disappeared in the presence of 0.l-O.6 M NaCl. Calf thymus nucleosome oxidized epinephrine rapidly, but the activity was negligible against norepinephrine, dopa and dopamine. These results indicate that calf thymus chromatin contains some substance (s) which oxidizes epinephrine specifically.