We studied 31 patients with acute herpes zoster (AHZ) 28 days' duration. Clinical characteristics (pain, allodynia. course of disease) and somatosensory perception thresholds (thermal discrimination, hot pain, and vibration) of the affected dermatome and the contralateral homologous area were assessed. Touch-evoked allodynia was found in 17 (55%) and dysesthesia in a further 5 (16%). Thermal and vibration perception thresholds demonstrated significant elevations when compared to the contralateral side. Thermal threshold abnormalities were significantly associated with the prevalence of postherpetic neuralgia (PHN) at 3 months. The effect of nerve blockade was less favorable on allodynia than spontaneous pain. The results of possible pathophysiological mechanisms are discussed.