Stimulus-sensitive hydrogels are polymeric materials which have a number of properties that make them interesting as materials for fabricating microsensors and microactuators, especially with respect to their swelling and shrinking behavior in response to a stimulus like pH or temperature. These properties include: low power consumption, good elasticity, simple hydrogel fabrication using cleanroom compatible UV-photolithography techniques and the fact that stimulus-sensitive hydrogels are powerful materials. In combination with pressure transducers, sensors can be made for gasses such as NH3 and CO2. The advantage of this type of sensor is the absence of a reference electrode that is used with electrochemical sensors. By using hydrogels as actuators, it should be possible to fabricate microactuators for valves and pumps that have superior closing properties and dust tolerance over conventional actuators. To overcome the issue of long response time constants we give a number of possible solutions such as the use of microspheres made of a stimulus-sensitive hydrogel.