In vitro comparison of 99Tc(m) antimony sulphide colloid and 99Tc(m) stannous phytate as well as in vivo studies in six rabbits and seven patients indicate disparity in the colloidal properties and localization of these two agents. The variability in lymphatic uptake and the relatively poor quality of scintigraphic images following interstitial injection of 99Tc(m) stannous phytate, when compared with 99Tc(m) antimony sulphide colloid, provide evidence of the unsuitability of this agent for lymphoscintigraphy. Maintenance of the diagnostic quality of the lymphoscintigraphic image and adherence to interpretive criteria already established therefore preclude the routine use of 99Tc(m) stannous phytate for interstitial lymphoscintigraphy.