The horizontal semicircular canal in pigeons was thermally stimulated with a miniature Peltier-element device. Sound evoked electric responses from the vestibular organ were modulated by the caloric stimulus. Experiments were performed under minimal influence of gravity, (horizontal canals in horizontal plane), and with the pigeons head tilted forwards or backwards. On the basis of the results it was concluded that the influence of gravity can be described by Bárány's convection theory. Extra effects are, however, present and they are most probably partly of mechanical origin (fluid expansion) and partly due to a direct influence of temperature on the vestibular receptors. Further experiments are needed to investigate the origin of these extra effects in more detail.