Recent developments in microsurgical techniques have brought about the possibility of restoration of the main branches of the cerebral arterial blood flow resulting from obstructive conditions. These arteries usually indicate pathological alterations.<br>However, there are only a few reports on the healing processes of the anastomotic sites on the pathological arterial wall.<br>In the present study, the histological and histochemical healing processes were investigated in an anastomotic site of normal and pathological arterial walls.<br>Ninety-two normal rats and 96 Goldblatt rats were used.<br>End-to-end anastomosis was performed on the left common carotid artery by microsurgical technique.<br>The patency rates of anastomosis were 71.6% in normal rats and 73.0% in Goldblatt rats. Patent anastomosed arteries were observed at various post-operative periods, ranging from 24 hours to 12 weeks. For histological studies, hematoxylin-eosin and Van Giesen stainings were used. For histochemical studies, lactic dehydrogenase, glucose-6-phosphate dehydrogenase, succinic dehydrogenase, cytochrome oxydase, acid phosphatase and alkaline phosphatase were examined.<br>Goldblatt rats were divided into two groups histologically. One group had a slight degeneration of the medial muscle, and the other group had a marked degeneration. This histological difference between the two groups was probably due to blood pressure. A histological examination revealed a healing stage at four weeks in the former group and the histochemical study showed healing at eight weeks in the former group. There was no significant difference on the healing process between the former group and normal rats.<br>Goldblatt rats which showed marked degenerative changes of the medial muscle indicated a poor healing process with granulation in the outer regions of medial necrotic areas. At 12 weeks after anastomosis, histological examination still showed the prominent and widespread degenerative changes on the medial wall. The histochemical examinations of this group revealed few enzymatic activities in the media in areas adjacent to the anastomosis, although rather higher activities were observed in the adventitia in granulation areas adjacent to the anastomotic site. But alkaline phosphatase in the adventitia around the anastomotic site markedly decreased in activity. These decreased activities of the alkaline phosphatase were probably due to destruction of the vasa vasorum.<br>These findings suggested that the cause of these prominent and widespread necrotic regions were due to the absence of circulating blood which was stopped by temporarily clipping and destruction of the vasa vasorum during the operation.<br>But, normal and slight degenerative arterial walls did not indicate such prominent changes.<br>It was suggested from these experimental study that the pathological arterial walls were easily injured in the ischemic condition during the operation.