In neurosecretory neurons of the hypothalamo-neurohypophysial system, the anterograde axonal transport of exogenous horseradish peroxidase taken into the cell body coincides wwth the anterograde movement of acid hydrolases. HRP laden dense bodies in neuronal perikarya are secondary lysosomes since HRP and acid hydrolase activity occur in the same dense body. When mice are given 2% NaCl to drink for 5 days, the number of acid hydrolase-positive lysosomes and cisterns in the neurosecretory cell body and axons is greater under hyperosmotic stress than in unstressed controls. The anterograde transport of HRP likewise increases in these stressed neurons. The HRP appears in structures similar to those with acid hydrolase activity. These cisterns closely resemble the agranular reticulum. In the soma, cisterns are confluent with secondary lysosomes. The confluence can provide the route through which acid hydrolases can leave perikaryal secondary lysosmes for transport down the axon. Acid hydrolase activity in the axon and terminals of the neurosecretory neuron would be elevated in response to hyperosmotic stress for degradative functions. The anterograde transport of substances slated for enzymatic degradation in perikaryal secondary lysosomes, would, therefore, be associated with the efflux of acid hydrolases from the secondary lysosome.