RFCNU or (chloro-2-ethyl)-l-(ribofuranosyl-isopropylidene-2', 3' paranitrobenzoate-5')-3 nitrosourea, a new synthetic nitrosourea derivative, which has been shown to have, in mice, among all nitrosourea derivatives tested, the longest maximallly efficient dose interval (MEDI) and which is not immunosuppressive at the smallest dose of MEDI, gave in a phase II trial on digestive tract tumours (at the dose of 400 mg/m2 per month determined by the phase I trial), 30% objective remissions among which 13% were greater than 50%.