The diagnostic efficacy of 99Tcm-labelled non-specific polyclonal immunoglobulin (IgG) as tracer for abdominal inflammatory lesions is impeded by its unfavourable physiological organ distribution patterns. Modifications to the IgG molecules during preparation and labelling may alter its in vivo behaviour and accumulation in inflammatory foci. This report describes scintigraphic biodistribution studies in the baboon (normal and with inflammatory lesions) of various thiol reduction-mediated 99Tcm-IgG preparations. These are human IgG (Sandoglobulin) where the Fc-mediated complement activity is impaired, human IgG (Gammagard) where the Fc portion is left intact, and baboon IgG isolated from the serum of each animal (autologous): the first two preparations are commercially available. Normal baboon organ distributions were obtained for each tracer over a period of 3 h, commencing 4 h after administration. Similarly, lesion-to-background ratios in thigh and abdominal lesions (bacterial and chemical) were compared. Mean normal organ distributions (n = 6) were relatively constant during this period. Kidney uptake with IgG (Sandoglobulin) was significantly enhanced, as was liver uptake with IgG (Gammagard) and the baboon IgG. Biodistribution pattern changes after lesion induction tended to be similar for IgG (Gammagard) and baboon IgG, where activity washout became more prominent. Lesion-to-background ratios in the thigh far exceeded those in the abdomen, except for the individual animal's own IgG which performed well in this case.