Results are presented describing serum caffeine half-lives for three healthy subjects and two patients having alcoholic hepatic disease. The mean serum caffeine half-life for the healthy subjects was 5.7 hours. One patient, a 35-year-old man who had alcoholic hepatic disease, had a serum half-life of 60 hours. The other patient, a 49-year-old woman having alcoholic hepatic disease had a serum half-life of 168 hours. The prolonged serum half-lives for the two patients are explained on the basis of compromised liver function. The serum half-life of caffeine was determined for the three healthy subjects when 25 mg diazepam was given one hour prior to the caffeine load. A significant difference was not found between the serum half-lives measured after diazepam was given and the serum half-life measured when diazepam was not given.