Composite piezoelectrics are very interesting as transducers for future medical devices. This paper compares the properties of ceramic-plastic composites and of porous ceramics with various structures of pores with each other. The emphasis lies on those properties that are important for the mentioned application. The properties of porous ceramics were calculated based on Bruggemann's theory, those of regularly structured composites were calculated with a cell model. Here, the discussion is restricted to the case where the composite can be considered as being a homogeneous medium. The results for the calculations agree well with the known measured values. It is shown that within all the treated composite classes one can find materials with a sufficiently high coupling factor (-0.5), a low lateral coupling factor, a low-quality factor (-151, and a low acoustical impedance (-8- lo6 kg/m2s). Composites with very fine internal structure are best suited for the application in ultrasonic antennas. Several production techniques are discussed. Among these, the photolithographic methods offer interesting possibilities for the preparation of composites.