The authors report the results of bismuth blood levels in 41 patients treated by oral route with bismuth salts used in gastro-enterology according to the Bensaude rule (10 to 20 g/day, 20 days/month). Median bismuth blood level during the period of treatment amounts to 13 microgram/l. It decreases to 7 microgram/l during the period of therapeutic withdrawal. In patients with bismuth encephalopathies (63 cases recorded in the literature) median values range from 680 to 700 microgram/l. The authors recommend the determination of bismuth blood levels as a monitoring method in bismuth treatment and propose the following values:--normal level during treatment : less than 50 microgram/l (in Bi metal);--alarm level : 50 to 100 microgram/l : (patients to be monitored);--toxicity level less than 100 microgram/l : (treatment to be interrupted).