Abstract: A pyroelectric sensor is provided for detecting enzymes or enzymatic substrates in a liquid or gas stream. The sensor contains a laminate formed of a pyroelectric material sandwiched between upper and lower conducting means to act as electrodes. An electronic circuit means is connected to the conducting means to measure thermally induced electric current and an enzyme or enzymatic substrate is immobilized on a surface of one of the conducting means. The laminate is supported by a support means and a plate means rests on an upper surface of the supported laminate. The plate means has a longitudinal flow channel communicating with the upper surface for flow of a gas of liquid, and a recess for accommodating the electronic circuit means. Inlet and outlet means pass through the plate means and communicate with the flow channel.