Abstract The appearance of neutron activated amosite fibres in lymph from right lymph duct and thoracic duct was measured in dogs following administration by intrabronchial instillation. Transfer was quantified using the associated radioactivity and in addition samples of lymph and of thoracic lymph nodes were examined by SEM 24 hours after administration. This showed that there was a fast translocation of fibres from the airspaces of the lung to the lymph nodes and even into postnodal lymph. Analysis of the fibres collected in lymph showed that both the structures of the peripheral lung and the lymph node itself act like size selective filters, permitting only the fine fibre fraction to penetrate. Fibres below about 9 μm in length and below about 0.5 μm in diameter can be cleared into the postnodal lymph and thus can reach any organ of the body. A model of size dependent fibrous particle clearance in the lung is described incorporating lymphatic as well as other pathways.