  The Alpha Magnetic Spectrometer (AMS) is a state of the art particle physics
experiment for the extraterrestrial study of antimatter, matter and missing
matter. AMS successfully completed the precursor STS91 Discovery flight (June
2nd-12th, 1998), completing 152 orbits at 52 degrees of latitude and about 400
km of height, collecting more than 100 million CR events. In this paper we
report on the first flight experience and we present preliminary results on the
search for nuclear antimatter. No antimatter nuclei with Z>=2 were detected. We
obtain a model dependent upper limit on the anti-He /He flux <1.14 10^^-6 In
the rigidity region between 1.6 to 20 GV we obtain a model independent,
conservative upper limit on anti-He /He flux <1.7 10^^-6 and <2.8 10^^-5 for
Z>2, improving the results of previous published searches performed with
stratospheric balloons.
