The role of the facial nerve latency test in the prognosis of Bell's palsy. Eighty patients with idiopathic facial nerve palsy were evaluated by the facial nerve latency test. Depending on the latency time, the patients were classified into the following four groups: group A patients had normal latency times (3.25 msec); group B patients had slightly extended latency times (4 to 7 msec) and a mean of 5.6 msec; group C patients had extended latency times (10 to 14 msec) and a mean of 10.2 msec; and group D patients displayed complete disappearance of evoked compound muscle action potential (no responses). Under the same therapeutic regimen, it was determined that, when the latency time was normal or close to normal, the functional recovery of the nerve was complete or almost complete, and the recovery time was short. When the latency time was extended or there was no response, the functional recovery of the nerve was either incomplete or absent. 