Acetylcholinesterase (AchE)-positive afferent axons in the mucosa of the cat urinary bladder were examined in the present experiments, Small-sized dorsal root ganglion cells containing AchE enzyme activity were labelled by injection of retrograde tracer (wheat germ agglutinin conjugated to enzymatically inactive horseradish peroxidase gold complex) into the bladder mucosa of adult cats, Results show that 48.9% (90/184) of the labelled ganglion cells possessed AchE enzyme activity. Following unilateral dorsal root ganglionectomy (L(2-5), S-1-3), a total of 6619 unmyelinated axon terminals were examined in the bladder mucosa, including 691 degenerating axon terminals, Percentages (8.6-16.1%) of degenerating axon terminals in the ganglionectomized animals (1, 2, 3, 10 and 21 days post-operated) were significantly higher than those of controls (3.1%) and the 60-day post-operated animals (3.2%). Approximately one-half (47.9%) of the degenerating axon terminals observed in the 1-21 day post-operated animals were AchE-positive. Further examination also disclosed that the population of the intact (not affected by ganglionectomy) AchE-positive axon terminals at 60 days (59.3%) was significantly greater than that of controls (45.6%). The AchE-positive terminals containing few synaptic vesicles were significantly increased in number in the 60 day post-operated cats. In conclusion the present study demonstrates that one half of afferent axons in the mucosa were AchE-positive, The increase in AchE-positive afferent axon terminals containing few synaptic vesicles may be derived from contralateral dorsal root ganglia resulting from sprouting following dorsal root ganglionectomy.