The pyroelectric properties of Pb1-xCaxTiO3 (x = 0-0.3) thin films have been greatly improved by including porosity in the microstructure. Control of nucleation and growth by variation of the heating rate was used to process porous, low dielectric constant films on platinized silicon wafers. Electrical characterization of poled films showed pyroelectric coefficients of up to similar to 200 mu C/m(2) K and permitivities as low as epsilon(r) approximate to 55. The resulting high figure-of-merit p/epsilon(r) in combination with small dielectric losses of 0.5%-2.0% at 1 kHz make the films good candidates for pyroelectric thin-film devices. Relationships between microstructure, composition, and properties were established. (C) 1998 American Institute of Physics. [S0003-6951(98)03119-2].