Brain dysfunction and blood flow velocity changes in the middle cerebral artery (MCAFV) were studied in 59 patients with ruptured cerebral aneurysms presenting subarachnoid hemorrhage. Brain function and blood flow velocity were evaluated by multimodality evoked potentials (MEPs) consisting of ABR, SEP and VEP as reported, and transcranial Doppler (TCD) ultrasound. The abnormality on MEPs were graded into 4 grades. Nearly normal, mildly abnormal, moderately abnormal and severely abnormal. The results on MEP study were compared with clinical Hunt and Hess (H. H) grade or Fisher's CT group of subarachnoid hemorrhage in 44 patients. MCAFV was measured in 15 patients and mean velocity as well as CO2 reactivity and effect of head elevation were studied. Control value of MCAFV was 64 +/- 13 cm/sec in 50 healthy adults. CO2 reactivity was determined by K values obtained from the modified formula of cerebral blood flow by Olesen et al. MEP grade in H. H grade III and IV patients showed, on admission, variations in their grades in comparison with those in H. H grade I II and V patients. There was no definite correlation between the abnormality in MEPs and the degree of subarachnoid hemorrhage in Fisher's group 3 and 4 patients. When the surgical results in early and late operation in H. H grade III and IV patients were compared, it was shown that the outcome was favourable in early operated patients of H. H grade III if initial MEP grades were between I-III.(ABSTRACT TRUNCATED AT 250 WORDS)