The present study was performed to determine whether renal efferent sympathetic neurons could be identified using a retrograde neuronal tracer without compromising renal function and whether the labeling and identification procedure alters Ca²⁺ currents and neuromodulation of those neurons. Renal sympathetic and superior cervical ganglion (SCG) neurons were labeled with the fluorescent retrograde tracer fast blue. Renal function studies made 1 wk after labeling revealed that renal hemodynamics and fluid and electrolyte excretion were similar between the dye-injected (left) kidney and the control (right) kidney under control conditions and after hemorrhage. After volume expansion, urine flow in the dye-injected kidney was slightly, but significantly, less than that of the control kidney, whereas urinary sodium excretion increased by approximately ninefold in both kidneys. Patch-clamp studies of SCG neurons in 10 mM external Ca²⁺ revealed that peak currents were not affected by the presence of the dye or a 1-min exposure to ultraviolet (UV) light. Neither maximal norepinephrine-induced Ca²⁺ current inhibition nor the sensitivity to norepinephrine was affected by the dye or 1-min UV exposure. Facilitation protocols revealed that G protein modulation of Ca²⁺ currents remained intact in dye-labeled UV-exposed neurons. This study demonstrates that a retrograde fluorescent dye technique to identify renal sympathetic neurons does not compromise renal function and the presence of the dye label or UV exposure has no effect on Ca²⁺ currents and neuromodulation in these neurons. Isolation of single identified renal sympathetic neurons coupled with patch-clamp techniques represents a tool to investigate the role of individual current systems in the modulation of excitability in these neurons, which play an important role in the control of renal hemodynamics and excretory function and in the pathogenesis of hypertension.