Three-dimensional (3D) x-ray microtomography is a technique for obtaining the 3D distribution of x-ray attenuation coefficients within small objects. To obtain microtomographic images apparatus has been developed which consists of a microfocal x-ray source, a computer-controlled stage for rotating the object, a 2D multi-wire gas proportional x-ray counter and a microcomputer to control image acquisition. Projection data were generated by rotating the object to discrete orientations around a single axis until of the order of 100 2D projection images of the object were collected. The projection images were transferred to a VAX 11/750 computer for subsequent 3D reconstruction using a convolution and back-projection algorithm in cone-beam geometry. The reconstructed data, comprising cubic voxels, may be displayed as sets of sequential transaxial, sagittal and coronal planes through the object. Alternatively, perspective displays of individual orthogonal sections may be formed with either intersecting planes or with these planes projected onto the surfaces of a box-like structure. The technique provides for the investigation of small-scale structures in biological specimens and we show some illustrative images of dead insects.