implantable enzymatic sensors for biochemicals such as glucose are provided having an ideal size and geometry for optional long term implantation and linear responses over the concentration ranges of interest . the sensors include an elongated body supporting an indicating electrode section having an appropriate enzyme immobilized thereon to present an enzymatic indicating surface . a permeable synthetic polymer membrane is applied over the sensor body to protect the enzyme and regulate diffusion of analyte therethrough , to ensure linearity of sensor response . the sensors are of flexible design and can be implanted using a catheter . alternately , the sensor includes an internal indicating electrode body housed within an apertured , hollow needle . a holder affixed to the needle allows for easy manipulation and implantation of the sensor .