Iodinated monoclonal antibody 96.5 was injected intravenously in the nude rat model transplanted with human melanoma. The activity distribution was evaluated by: 1) direct application of dissected tissue on autoradiographic film, 2) autoradiography of whole-body sections, and 3) beta-camera imaging of fresh frozen tissue. Method (1) is non-quantitative and has a poor resolution. It can only be recommended for simple screening. The whole-body method (2), although complicated, gives more accurate digital information of tissue uptake in individual pixels, or in larger regions of interest (ROIs). The beta camera technique (3) is a rapid method but its accuracy is less than the whole-body method. All three methods showed that the activity distribution in the tumours was more heterogenous than in other tissues. An overlap of activity uptake in tumours and other tissues was often seen. Mean uptake ratios in the whole body autoradiograms correlated well with in vivo uptake ratios from measurements in dissected tissues. At present, whole body autoradiography appears to be the method of choice for imaging the uptake of radiolabelled monoclonal antibodies in experimental animals.