An implantable nuclear magnetic resonance spectrometer for measuring the chemical composition of a fluid or for measuring the flow rate of the fluid. The spectrometer includes a housing and a catheter traversing across the housing so that a fluid external to the housing may flow through the catheter within the housing. A permanent magnet is disposed within the housing and generates an intense homogenous magnetic field in the vicinity of the catheter. An electronic circuit is disposed within the housing for detecting and formatting a nuclear magnetic resonance excitation signal. An excitation coil is connected to the electronic circuit and is disposed about the catheter to expose the fluid within the catheter to the excitation signal and to collect the nuclear magnetic resonance excitation signal.