The biological effect of a radiopharmaceutical depends heavily on the heterogeneity of the uptake in the various tissues. A comparative study of two radiopharmaceuticals should therefore include a comparison of the uptake patterns in different tissues. To eliminate the problems caused by variation in kinetics and tumour characteristics between individuals, such a comparison should be based on measured distributions of the radiopharmaceuticals in the same tissue sample. The excellent linearity between activity and counts in images obtained with a digital silicon strip detector allows such distributions to be derived from two autoradiographs acquired at different time points. This method was applied in a comparison of the uptake patterns of 153Sm-EDTMP and 89SrCl2 in sections obtained from a dog with spontaneous osteosarcoma, containing both tumour and normal bone tissues. As the areas of the section were larger than the detector area, the section had to be cut into smaller parts. Images of these were later merged by means of image processing techniques. There were significant differences in the uptake patterns of the two nuclides. In the primary tumour, the uptake of 153Sm was highly heterogeneous, while 89Sr was more uniformly distributed. In trabecular bone, the accumulation of 153Sm was higher than that of 89Sr. In solid cortical bone, 89Sr had the highest uptake.