A time-gated fluorescence-imaging technique was applied to study the distribution of sensitizer in porphyrin-treated tumour-bearing mice. The animals were administered with either haematoporphyrin derivative (HpD) or Photofrin and sacrificed 4 or 12 h later. Fluorescence images were acquired from tumour, skin, muscle, fat, brain, lymph node, bowel and bone of both treated and untreated mice. The results obtained with HpD and Photofrin are similar. In images acquired 30 ns after excitation a bright exogenous fluorescence allows clear detection of the tumour. Nevertheless, the images show that porphyrins localize with different concentrations in all the examined tissues except the brain. Moreover, an appreciable long-living endogenous emission was observed in the bone.