Abstract Forty-four image-tube spectra of YY Gem (4 Å mm−1, λλ 4820–4900 Å) are analyzed to yield the radial velocity curves and the variations in the intensity and the width of Hβ emission lines during the quiescent phase at epoch 1978 January 4–8. The present study disagrees with the claim by Leung and Schneider (1978) that the orbital period of the YY Gem system has substantially increased. The intensity weakly varies in a single-wave mode over an orbital period for the primary, while it strongly varies in a double-wave mode for the secondary with the maximum around phase 0.7 corresponding to the phase of the “star spot” phenomenon. The analysis confirms the finding by Bopp (1974b) that the amplitude of the radial velocity curve derived from emission lines is larger for the primary than for the secondary. This anomaly is interpreted in terms of non-axisymmetric sectorial distributions of the emission intensity on the stellar surfaces subject to synchronous rotation. The variation of the intrinsic line widths in a double-wave mode, common to both components, suggests an influence of the orbital motion on internal motions in the active regions. The internal motion within the Hβ-emitting regions is found to be about 20–30 km s−1 on an average.