The effect of the possible influence of a new calcium antagonist, PY 108-068, on regional cerebral blood flow (CBF) was studied in patients suffering acute ischemic stroke. The dosage was 1.5 + 2.5 mg intravenously in six patients (series 1) and 2.5 + 5.0 mg intravenously in five other patients (series 2). CBF was measured before and after treatment by xenon-133 inhalation and single photon emission computed tomography (Tomomatic 64). In the first series, no changes in hemispheric CBF, arterial blood pressure, or clinical symptoms were noted after treatment, but one patient showed an increase of CBF in part of the peri-infarct area. In the second series, slight increases in mean hemispheric flow values were seen, but in three of the five patients CBF decreased even further in the ischemic area. Arterial blood pressure decreased by 13%, and the clinical symptoms were unchanged. In conclusion the results shows, that calcium antagonist may be harmful in acute ischemic strokes since it can decrease the cerebral blood flow further in the ischemic areas. A potential beneficial metabolic effect of an calcium antagonist in ischemic tissue may thus be overshadowed by a harmful flow decrease.