Radio transmitters were surgically implanted into the abdomens of red foxes (Vulpes vulpes). Blood samples were taken before, immediately after, and 8 hr after surgery and analyzed for hormonal, biochemical, electrolyte and hematologic changes. Samples were taken at the same times from control foxes. Adrenocorticotropin increased after surgery (P < 0.05), but returned to pre-surgery values after 8 hr. Cortisol increased and remained elevated in the surgery group relative to pre-surgery values or to control values (P < 0.05); Triiodothyronine and thryroxine both decreased from post-surgery values 8 hr later (P < 0.05). Creatine kinase, total bilirubin and aspartate aminotransferase increased after 8 hr in both surgery and control groups (P < 0.05). Carbon dioxide increased under anesthesia in both groups, but returned to initial values after 8 hr (P < 0.05). The white blood cell count increased after 8 hr only in the surgery group (P < 0.05). There were no differences between the groups for any value obtained from the initial blood sample. These data indicate that abdominal surgery results in prolonged adrenocortical activity and decreased thyroid hormone levels, but otherwise has minimal systemic effects in red foxes.