A previous field study concerning electronic navigation aids showed the advantage, in terms of navigational errors, of auditory presentation of route guidance instructions as compared to visual instructions (see W. B. Verwey and W. H. Janssen, 1988). In the present work, an experiment that tries to approach the issue of optimal route instructions in a more controlled environment is reported. Under conditions of severe perceptual-motor load, subjects were to interpret route instructions with slides depicting real-world junctions. The results showed the advantage of verbal over spatial information. No significant effect of presentation modality was found. Implications for presentation of route guidance instructions are given.