In 45 cases of sudden infant death syndrome (SIDS) in which unsuccessful attempts at resuscitation had been made and in 21 cases without attempted resuscitation, systematic histological investigations were carried out on the thymus. In these investigations, petechial hemorrhages were detected in 82% of the cases with attempted resuscitation and in 76% of the cases without attempted resuscitation. The histological distribution pattern of the petechial thymus hemorrhages did not differ notably between the two groups. The pattern of findings indicates that the hemorrhages had already developed during the death agony and that the typical histological distribution pattern with an increased occurrence of petechial in the cortical zone was altered by massive attempts at resuscitation in individual cases.