The Alpha Magnetic Spectrometer (AMS) was flown on the space shuttle Discovery during flight STS-91 in a 51.7• orbit at altitudes between 320 and 390 km. A total of 2.86 × 10 6 helium nuclei were observed in the rigidity range 1 to 140 GV. No antihelium nuclei were detected at any rigidity. An upper limit on the flux ratio of antihelium to helium of < 1.1 × 10 −6 is obtained.Submitted to Phys. Lett. B
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