Simple inexpensive methods are described for implanting chronic arterial cannulas for remote stress-free blood sampling of conscious unrestrained rats and for delivering acute isocapnic hypoxia to these rats in their home cages. The day before experimentation cages were placed in plastic bags with air (21% O2) flowing through at 15 1/min (normoxia). The next morning either normoxia was continued or isocapnic hypoxia (arterial PO2 38 Torr, arterial PCO2 38 Torr) was administered without handling or disturbing the rats. Repeated arterial samples were collected for measurement of blood gases, hematocrit, corticosterone, and ACTH. Blood pressure increased transiently (by 10 mmHg at 10 min) and plasma corticosterone and ACTH levels increased fivefold; hematocrit and heart rate did not change significantly. In rats receiving normoxia, all of these variables remained low. This preparation is useful for studying in conscious rats the regulation of endocrine systems easily stimulated by handling and for studying endocrine and cardiovascular adaptations to environmental stimuli such as hypoxia.