To determine its suitability as a lymph node imaging agent, 99Tcm dextran (99TcmDx) was compared with 99Tcm antimony sulphide colloid (99TcmSb2S3) in rabbits and dogs. In two groups of five rabbits each, absorption from the interstitial injection site, popliteal lymph node sequestration and total body uptake and distribution of both agents were determined. In three dogs, both agents were studied simultaneously, 99TcmDx and 99TcmSb2S3 being injected into the left and right hind feet respectively; therefore, only popliteal lymph node sequestration and image qualities were evaluated. Uptake curves in the rabbits indicated that total body uptake of 99TcmDx is faster and greater than that of 99TcmSb2S3. In spite of rapid lymph node uptake rates, total popliteal lymph node sequestration of 99TcmDx is significantly lower than that observed for 99TcmSb2S3. While lymph node uptake of 99TcmDx in dogs is higher than in rabbits, disparity between the two agents persists and is demonstrable in the image in both species. Reduced lymph node sequestration of 99TcmDx may result from its non-colloidal nature as well as its instability, both of which render this agent unsuitable for imaging pathological features of lymph nodes although its rapid absorption and distribution may be ideal characteristics for the study of lymphatic kinetics.