To develop an index of the activation of abdominal sympathetic nerves, we used Fos immunostaining of the celiac ganglion (CG) taken from rats receiving nicotine, preganglionic nerve stimulation, or glucopenic agents. Subcutaneous nicotine injection moderately increased Fos expression in the principal ganglionic cells of the CG (17 ± 4 Fos+ per mm², ~12% of all principal CG cells), whereas subcutaneous saline had no effect (0 ± 0 Fos+ per mm²; n = 7; P < 0.01). Greater Fos expression was obtained by applying nicotine topically to the CG (71 ± 8 Fos+ per mm²; 52% of all principal CG cells, n = 5; P < 0.01 vs. topical saline, n = 4) and by preganglionic nerve stimulation (126 ± 9 Fos+ per mm²; 94% of all principal CG cells, n = 11; P < 0.01 vs. nerve isolation, n = 7). Moderate Fos expression was also observed in the CG after intraperitoneal 2-deoxy-D-glucose (2DG) injection (21 ± 2 Fos+ per mm²; 16% of all principal CG cells, n = 5; P < 0.01 vs. saline ip) or insulin injection (16 ± 2 Fos+ per mm²; 12% of all principal CG cells, n = 6; P < 0.01 vs. saline ip). Furthermore, Fos expression induced by 2DG was dose and time dependent. These data demonstrate significant Fos expression in the CG in response to chemical, electrical, and reflexive stimulation. Thus Fos expression in the CG may be a useful index to describe various levels of activation of its postganglionic sympathetic neurons.