A surface-treatment technique using primary explosive was applied to a 316L type stainless steel. Some characterizations of the induced mechanical or metallurgical effects are given such as surface roughness, microhardness, residual stresses, microstructure. Fatigue tests were performed in tension-compression in the plastic strain-controlled mode with amplitudes in the range 10(-3) to 5 x 10(-3). The cyclic behaviour of the treated samples is characterized by a higher cyclic stress amplitude than the untreated material and a shorter fatique life. The surface damage has been analysed by counting the secondary microcracks after failure. The cyclic behaviour and the damage are discussed taking into account the different induced effects and assuming the treated material to be a composite one, with a highly strengthened surface layer and a quasi-untreated bulk.