The membrane potentials of astrocytes in primary cultures prepared from neonatal rat cerebral cortices were depolarized by (-)-norepinephrine. The average first response to 10(-5) M (-)-norepinephrine was 24 mV from an average resting potential of -68 mV, and the average for the second response was 14 mV. Thus this process showed marked desensitization. The response was attributed to an activation of an alpha 1-receptor since it was about 1000 times more sensitive to inhibition by prazosin than to yohimbine or idazoxan. In addition, depolarization was seen to the application of 10(-5) M phenylephrine.