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This paper compares the RBE of a neutron beam produced by 50 MeV deuterons on beryllium [d(50)-Be] at the cyclotron CYCLONE of Louvain-La-Neuve and of a neutron beam produced by 34 MeV protons on beryllium [p(34)-Be] of the Hôpital Régional d'Orléans. Early intestinal tolerance in mice was choosen as biological criterium; it is derived from LD50 determination after single and fractionated abdominal irradiation. For d(50)-Be neutrons, RBE was 1.8 +/- 0.2 (with respect to 60Co gamma-rays) for a single fraction. It increases up to 2.1 +/- 0.2 for an irradiation in 2 fractions (3.5 h interval) and reaches 2.5 +/- 0.3, 2.7 +/- 0.3 and 2.5 +/- 0.3 for irradiations in 10 fractions (7 and 3.5 h interval) and 20 fractions (3.5 h interval) respectively. RBE values observed for p(34)-Be neutrons (with respect to 60Co gamma-rays) are not significantly different. For a single fraction RBE = 1.7 +/- 0.2 and for 2 fractions (3.5 h interval) RBE = 2.0 +2- 0.2.