Twelve experienced navigators participated in an experiment to determine the effects of alcohol, caffeine, and an alcohol + caffeine mixture on performance during the following tasks: visual search, the search and location of items on a navigational chart (chartsearch) and the solving of maritime navigational problems. Alcohol (75 ml) produced impairment in performance on visual search (p< 0.05) and navigational problem-solving (p< 0.01). Caffeine was found to enhance performance on visual search (p< 0.05) but not on the chartsearch, although a significant correlation was found between performance on the two tests (p< 0.05). Caffeine was not found to improve the accuracy of navigational problem-solving (p> 0.05). Neither alcohol nor caffeine had any significant effect on the speed of problem-solving (p> 0.05).