A prototype of a combined CT–SPECT tomograph for breast cancer study has been developed and evaluated. It allows to perform scintimammography and X-ray CT in the same geometrical conditions. The CT system is based on a quasi-monochromatic beam tuned at 28 keV and an array of ultra fast ceramic scintillators coupled to photodiodes whilst the SPECT system is based on two scintillator matrices coupled to position sensitive photomultipliers. CT and SPECT sinograms of a test phantom were recorded and reconstruted with both modalities. Image fusion of CT and SPECT images was then performed. The developed CT–SPECT prototype is able to detect a region of interest of 1 cm 3 , with a 10:1 tumour/background concentration ratio, within an object having a diameter of 8 cm. r 2002 Elsevier Science B.V. All rights reserved.