[en] After participating in a several experiments near the reactor at Bugey, at distances from 15 to 100 m from the reactor the laboratory joined a collaboration for search of effect of neutrino oscillations at longer distances (1 km) from the neutrinos' point of origin. The zone covered by this experiment raises a particular interest because the results of several underground experiments on the atmospheric neutrinos indicated that oscillation could appear in this zone. The Chooz collaboration, reported here, joined three American universities (Philadelphia, New Mexico and Irvine), two Italian universities (Pisa and Trieste), the Kurchatov Institute in Moscow and two French laboratories (the LAPP in Annecy and the College de France). The first data have been recorded during the autumn of 1996 prior to the commissioning of the reactors (2 x 4200 MW_th), to measure the background noise. The detector is a target of 6 t liquid scintillator doped with Gd, sunk in 120 t non-doped liquid scintillator separated by thin transparent wall. The target is viewed by 192 photomultipliers. The scintillator liquids are carried up to the detector and then to the exterior tanks by a tunnel of 200 m length and a height gradient of 15 m. The fragility of the detector imposes a simultaneous filling of its components, with an accuracy of the order of 1 cm. A 200 MHz sampling system of the photomultiplier pulses signing the neutrino interaction was developed in order to obtain simultaneously information on the pulse-height, timing and shape. This experiment could serve as a prototype for heavier experiments conceived in US, in Russia at Rovno and Krasnoyarsk, and in France, at 15 km from the Perry reactor, at 500 m underground. Still more ambitious is the Japan project at Kamioka, at 160 m distance from a nuclear reactor. The experiment at Perry will push the electron neutrino upper mass estimates down to 0.01 eV