Studies dealing with the effects of alcohol on critical flicker fusion (CFF) are reviewed. The conclusion is drawn that relatively low doses of alcohol produce a decline in the flicker fusion threshold in normal subjects. Further, data are presented regarding the effects of alcohol on CFF in 32 male alcoholics. A decrement in the CFF threshold did not occur in alcoholic subjects given 8 to 10 ounces of vodka. This result suggests that CFF may be an objective measure of alcohol tolerance.