A method for pinhole emission computed tomography (ECT) using the image-processing capabilities of a gamma camera system is described and evaluated. The tomographic imaging capability of the method was assessed by studies of phantoms and its practical use by the distribution of inhaled 99Tc(m)-labelled aerosol particles in rabbits. The phantom studies demonstrate the tomographic properties in central and non-central planes. A reconstructed resolution of 4.4 mm (FWHM) and an overall homogeneity of +/-10% was obtained for a radius of rotation of the pinhole of about 8 cm. Pinhole ECT showed the distribution of inhales particles to be considerably different in two rabbits, subjected to different modes of mechanical ventilation. In planar images, on the other hand, it was difficult to appreciate the difference.