[Objective] I reported that a negative reaction time slope on display size 5 to 10 and a V-shape search function of the task result indicate prefrontal injury (p<0.001)(SFN abstract,26(2): 2232, 2000). In the present study, KN-VST and Wisconsin Card Sorting Test (WCST) were compared, from viewpoints of clinical applicability in the elderly who were substantially pre-demented. [Subjects/Method] Subjects were 31 healthy aged, who volunteered to participate in the University health check program of the elderly, including two suspected of dementia and eight slightly demented. Using 123I-IMP SPECT, sensitivity, specificity, and false positive/ negative rates were compared between KN-VST and WCST.[Result] KN-VST showed a splendid result (Table); higher sensitivity 87.5%/ specificity 86.7%, and lower false positive/ negative rates, while WCST showed much poorer results. [Conclusion] KN-VST has a splendid clinical applicability for detecting frontal lobe damages and has a reliable validity for a frontal lobe scree...