In flight exposure to nicotine, urinary cotinine and symptom self-reports were assessed in a study of 9 subjects (5 passengers and 4 attendants) on four routine commercial flights each of approximately 4 hours duration. Urine samples were collected for 72 hours following each flight. Exposures to nicotine measured during the flights using personal exposure monitors were found to be highly variable, with some nonsmoking areas attaining levels comparable to those in smoking sections. Attendants assigned to work in nonsmoking areas were not protected from smoke exposure. The type of aircraft ventilation was important in determining the levels of inflight nicotine exposure. The environmental tobacco smoke levels that occurred produced measurable levels of cotinine (a major metabolite of nicotine) in the urine of passengers and attendants. Passengers who experienced the greatest smoke exposure had the highest levels of urinary cotinine. Changes in eye and nose symptoms between the beginning and end of the flights were significantly related both to nicotine exposure during the flight and to the subsequent urinary excretion of cotinine. In addition, subjects' perceptions of annoyance and smokiness in the airplane cabin were also related to inflight nicotine exposure and urinary excretion measures.