By scanning electron microscopy the otolith membranes of the sacculus and utriculus of adult guinea-pigs were examined. The spatial arrangement of otoconia was found to differ from the standard scheme. New forms of imperfect otoconia were detected. Differences in morphological parameters of otoconia in the labyrinthine structures were revealed. Factors responsible for the development of imperfect otoconia on the otolith membrane are described and their relation to the potential changes in the sensitivity of otolith receptors is discussed.