1. Histochemical observations of the aerobic metabolism of the accessory boring organ (ABO) of Urosalpinx showed that cytochrome oxidase, succinate dehydrogenase and lactate dehydrogenase activities are localized in the secretory cells of the distal secretory disk.2. Correlated biochemical assays of cytochrome oxidase activity of whole homogenates of the ABO prepared from active snails gave specific activities which ranged between 0.190 to 2.10.3. There were no differences in cytochrome oxidase specific activities using ABO whole homogenates from resting or drilling snails. However, the specific activities of mitochondrial-rich particulate fractions isolated from whole homogenates by high speed centrifugation showed that oxidase activities of drilling specimens were 1.040 as opposed to 0.639 for samples from resting specimens.4. Snails did not bore shells of the oyster Crassostrea virginica when maintained in a N2 atmosphere, and ceased boring begun prior to transfer to anaerobic conditions.5. These data and observations were discussed in relation to physiological and ecological factors involved in predation and demineralization activities by Urosalpinx.