Sympathetic ganglion cells in vivo are understood to receive two types of ongoing synaptic input: ‘strong’ (>20 mV) and ‘weak’ (typically <5 mv) unitary EPSPs (2). From intracellular recordings of rat cervical sympathetic ganglion (SCG) cells in vivo, McLachlan et al. concluded that every cell receives 1 or 2 strong inputs, which are always suprathreshold (2). These cells also receive perhaps 5-10 ‘weak’ inputs, which rarely sum to reach threshold and so have little effect on postganglionic spike activity (2). SCG neurons are functionally heterogeneous, however, and few cells studied to date could be confidently labelled as vasomotor (3). We sought to study the properties of a larger, more homogeneous sample of vasomotor ganglion cells in vivo. In 20 urethane-anesthetized rats (1.4 g/kg, i.v.), the L3 ganglion was mobilized, keeping its rostral connections intact, pinned to a platform and bathed in Krebs’ solution. We made sharp electrode recordings from 43 lumbar sympathetic ganglion cells with ongoing spike activity. Technically satisfactory recordings lasted from 90 s to > 1h. Resting membrane potentials were -47±1.3 mV, and action potential amplitudes 71±2 mV. In addition to ongoing spikes, 40/43 cells had subthreshold EPSPs (mean rates 2.8 and 3.6 Hz, respectively). None had IPSPs. In 39/43 cells, spike occurrence was very strongly modulated by the cardiac cycle, indicating that they were of muscle vasoconstrictor (MVC) type (1). Their subthreshold EPSPs also showed this pattern, so we infer that their inputs were selectively from MVC-type preganglionic neurons. Where spikes lacked cardiac rhythmicity (4 cells), so did subthreshold EPSPs (present in 2/4). Inspection of the potential trajectory leading to spikes revealed that they were triggered by 3 or more distinct unitary EPSPs in 19/39 MVC-type ganglion cells. Small EPSPs very rarely summed to reach threshold. Observations on EPSPs after blocking spikes with hyperpolarizing current confirmed these conclusions. Another new finding was the common occurrence of intermediate-sized (10-20 mV) unitary EPSPs in 16/39 MVC-type cells. These were not far below threshold (estimated as ~18 mV above resting potential). Our data thus confirm that ‘strong’ EPSPs essentially determine spike activity in putative vasomotor ganglion cells, leaving little room for synaptic integration. Convergence of strong preganglionic inputs is greater than previously suspected, however, and the existence of ‘intermediate’-sized EPSPs provides the potential to enhance ganglionic throughput by a modest change in cell threshold.