Аннотация:From spectroscopic and photometric observations of HD 209961 = V365 Lac in 1986-1988, it is confirmed that this star is an ellipsoidal variable. From a solution of the radial-velocity curve and an analysis of the optical light curve, the parameters of V365 Lac are determined: q = 0.6-0.65, i = 38-46 degrees, M1 = 17 M(sun), M2 = 11 M(sun). It is concluded that the secondary component in the system is a normal star of spectral type ~B2 V, about five times fainter than the primary component in the optical range, rather than a compact object surrounded by an accretion disk. The radii of the stars are close to the boundaries of their Roche lobes. The system is apparently a contact binary.