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Because of numerous close coincidences with important ZrO bandheads, it is difficult to determine conclusively the presence or absence of bands of NbO in spectra of S-type stars. The only bands which appear favorable for detection of NbO are X 6484 and X 6591. These appear to be weakly present on a spectrogram of R Cygni taken at a cool phase.The abundance ratio, Nb/Zr, presumably varies during the synthesis of Tc (Anders 1958; Amould 1967). The importance of determining relative abundances of Zr, Nb, Mo, Tc, and Ru in cool stars has already been stressed (Davis 1968). This would be a very extensive project. In the present paper we shall be concerned only with niobium.