When rats immunized with bovine serum albumin in complete adjuvant were irradiated 10 days later with 800 rads their ability to display a positive skin reaction to the test antigen was suppressed for 4–5 days. Thereafter recovery was evident in spite of persisting low blood leucocyte levels. Specific cells were demonstrated in the animals by migration inhibition of peritoneal cells two days after irradiation, when skin reactions were negative. On the other hand transfer of normal bone marrow cells corrected the ability to mount skin reactions but spleen, thoracic duct or lymph node cells did not. It seems that post‐irradiation suppression of skin reactions does not depend on damage of specific cells but depends on shortage of a bone marrow derived cell type participating in skin reactions as a nonspecific compon