Type B neurons of the bullfrog sympathetic ganglia were examined to confirm the existence of axon collaterals and the distribution of synaptic contacts using the intracellular horseradish peroxidase (HRP) labeling method. The mean diameter of the perikarya was 60.8 (+/- 11.5 standard deviation; n = 36) X 43.8 (+/- 11.3) microns and the mean diameter of the initial segments of axons was 6.0 (+/- 1.8; n = 36) microns. Axon collaterals were found in 6 cells among 36 examined. They branched from axons at 61-167 microns from the perikaryon of origin. Short-axon collaterals containing vesicles (diameter: about 70 nm) were also observed to protrude from the stem axons. Spine-like processes were observed from the cell soma, axon hillock and the initial segment of the axon. They enclosed synaptic axon varicosities, or extended into the extracellular space without any synaptic contact. Serial sections revealed 171 axon varicosities in contact with a single ganglion cell; 32 (18.7%) varicosities were seen on the somata. 66 (38.6%) on the axon hillock and 73 (42.7%) on the initial segment of the axon which extended 100 microns from the perikaryon. Synaptic terminals were also found on the axon as far as 494 microns from the cell body of origin. These findings would provide a morphological basis for interaction between bullfrog sympathetic neurons at pre- or postsynaptic sites.