A number of characteristic sources of error during the testing of vestibular function, originating from anamnesis, equipment and examination, are described. It is stressed that false-positive findings are often due to the influence of alcohol and that false-negative findings may be the result of tiredness or sedative drugs. With regard to the caloric test, it is recommended that water provides a better stimulus than air, and that the warm caloric stimulus is more valid than the cold caloric stimulus. Attention should be paid to the ENG-recorders, particularly to an adequate writing breadth, and to time constants. Different parameters in use for quantitative analysis of the intensity of vestibular reactions are discussed. If the findings are vague, repeated examination will often help to clarify matters. The regular use of Frenzel glasses is of great importance, since otherwise examination of the vestibular organs must be considered incomplete.