Observations of light elements in massive stars

Observations of light elements in hot massive stars are limited to few transitions of boron in the satellite-ultraviolet; lithium and beryllium are not observable at all. But because of its high sensitivity to the effects of rotational mixing, boron abundance determinations in massive stars have excelled as the definite test for evolutionary models with rotation. In this paper the observational evidence for rotational mixing in massive stars is reviewed and alternative interpretations are discussed.