In this study we investigated the influence of laser energy on the rheological properties of blood passing through the superior sagittal sinus. Twenty-two guinea-pigs were used. In the control group craniectomies were done and only the superior sagittal sinuses were exposed. This procedure had no significant influence on haematological factors and erythrocyte deformability. In the experimental group a carbon dioxide laser application was applied to the parasagittal brain tissue. In this group MCR, MCHC values and erythrocyte deformability were found to be changed singificantly.