123I-IMP SPECT and CT were evaluated in 20 patients with closed-head injury. The detected focal lesions by both examinations were 36. Twenty lesions (55.6%) were seen on both CT and SPECT, and SPECT revealed larger abnormality than CT. Sixteen (44.4%) of 36 lesions were seen only on SPECT. Regional cerebral blood flow (r-CBF) of thirty-one focal lesions were quantified by reference sampling method and compared to r-CBF of the patients without neurological problem. r-CBF of 18 localized lesions accordant with low density area (LDA) on CT were significantly lower than those of 13 lesions seen only on SPECT. And r-CBF of both lesions were significantly lower than that of control patients. Regional cerebral blood flow on the areas with visually normal RI uptake were also significantly lower than that of control group. Regardless of CT findings, some disturbance of r-CBF was considered in patients with head trauma. Therefore the quantification of r-CBF with 123I-IMP SPECT was a useful method for evaluating functional change in those patients.