Informed consent in phase I trials involves very difficult problems related to experimental factors of the phase I trial, a toxicity study conducted in human cancer patients. However, this is the first clinical step in new drug development, and patients must participate in phase I only when there is full disclosure of correct trial information. Disclosure should include the purpose of the trial, the procedure, and the risk/benefits related to the trial. Informing the patient of the cancer diagnosis and the extent of disease is also necessary before entry into a phase I trial. Although phase I trials are conducted with the precious contribution of patients, it is important that informed consent should not become a type of legal contract. Informed consent in phase I trials is an essential process, just like a roundtable discussion of patient and physician before fighting an incurable cancer.