  The orbits of five single-lined spectroscopic binaries have recently been
determined. We now use astrometric measurements that were collected with the
Hipparcos satellite to constrain the systems' mass ratios and secondary masses.
The barycentric astrometric orbits of three binary systems, HD 140667, HD
158222, and HD 217924, are fully determined and precise estimates of their mass
ratios are obtained. Follow-up of these systems with infrared spectroscopy
could yield model-independent dynamical masses for all components.
