Deep brain stimulation (DBS) is used to alleviate tremor in patients diagnosed with Essential Tremor who do not respond to conventional treatments. To achieve optimal tremor suppression, a large stimulus parameter space needs to be explored. In practice, a default pulse duration and stimulation rate (generally 60 us and 130 Hz) are often chosen and current or voltage varied to determine a clinically effective setting. This study explored the effect of rate of stimulation in 5 patients with bilateral DBS stimulation to the posterior sub-thalamic area (PSA). Additionally, the effects of varying charge per pulse by varying pulse duration alone or by varying current/voltage alone were compared. In experiment 1, rate was varied using the values 20, 70, 100, 130, 150 and 210 Hz, keeping pulse duration (90 us) and current (1 patient) or voltage (4 patients) fixed. In experiment 2, rate was fixed at 130 Hz, and charge per phase was varied first by changing pulse duration between 60, 90, and 120 us, and secondly by altering current or voltage by the same ratios. Tremor severity was categorized by two experienced clinicians. Figure 1 shows the effect rate for each subject. A repeated measures ANOVA showed a significant effect of rate (p <0.001) with the 40 Hz rate producing worse tremor scores than all rates of 100 Hz and above. Two patients showed a U-shaped response with best tremor suppression between 100 and 130 Hz, whereas the remaining patients showed a trend for better tremor suppression as rate increased across the whole range. Paired t-tests showed no significant difference between changing charge per phase via pulse duration or current/voltage, although both these effects were small, leading to poor statistical power.