In 41 out of 130 encapsulated chronic subdural haematomas erythroblasts were found. As there were no skull fractures and no erythroblasts were found in peripheral blood smears, it is concluded, that these colonies of erythroblasts originate from the granulation tissue during the formation of membranes. The actual output of mature erythrocytes is not known. The influence of erythroblasts on the clinical course of chronic subdural haematomas is uncertain.