A systematic study of vitamin C blood levels in patients with cancer and an evaluation of their modifications when the patients were orally treated with daily large doses of ascorbic acid (5g/day) have been carried out. For excluding any interference on intestinal vitamin C absorption, all patients with digestive tract cancer have been excluded. Our first results concern 24 lung cancer and 35 bladder cancer patients, operable or not, of different sex and age. The study has shown hypovitaminosis C subclinic conditions for the greater part of subjects: in fact the average haematic rate of ascorbic acid approaches to lower level of physiologic range, appearing very low particularly for the younger patients. Periodic haematic dosages of vitamin C of unoperable and operated patients treated with large doses of ascorbic acid, have shown a rapid increase of its blood concentration which frequently has been very over 1500 micrograms%, the higher level of normal range. These high vitamin haematic levels, generally constant during the time, appear usefull in increasing the defence reactions of the cancerous patient.