The results of the investigations on the mechanism responsible for the formation of helium lines in the quiescent solar atmosphere are discussed. The observations were performed on 16 and 17 January 1997 by the coronal diagnostic spectrometer (CDS) and the solar ultraviolet measurement of emitted radiation (SUMER) onboard the Solar and Heliospheric Observatory (SOHO). The statistical properties of the helium spectrum and the constraints that such observations bring up are discussed.