The influence of the stimulus medium in thermal vestibular tests has been investigated by many authors, comparing nystagmus reactions after air and water irrigations. We first measured temperature changes in the ear canal and in the horizontal semicircular canal after both kinds of stimuli, using human temporal bone preparations, which were placed in a water bath of 37 degrees C. Irrigations were done with air of 45 and 27 degrees C with a flow of 5 l/min during 45 s and with 100 ml water of 44 and 30 degrees C during 30 s. The maximum temperature changes in the ear canal are almost equal after both kinds of irrigation (see Figs. 2 and 3). The change of temperature, however, lasts longer after water irrigation. The time constants are 20 and 57 s for the decay after warm and cold water irrigation and 9 and 20 s after air irrigation, respectively. The maximum temperature change in the lateral part of the horizontal semicircular canal is 0.4 and -0.3 degree after warm and cold irrigation with water. The corresponding values after irrigation with air are 0.1 and -0.15 degree. In addition, we investigated the effect of irrigating temporal bone preparations with perforated tympanic membranes (Fig. 4). After irrigation with air of 45 degrees C, the temperature in the horizontal semicircular canal decreased due to evaporation of humidity in the tympanic cavity. The equipment of choice for the irrigation of such ears is a stimulator reported by Scherer, where water flows through a silicon bubble which coats the ear canal.(ABSTRACT TRUNCATED AT 250 WORDS)