  We present full-polarization VLBA maps of the ground-state, main-line, 2 Pi
3/2, J = 3/2 OH masers in 18 Galactic massive star-forming regions. This is the
first large polarization survey of interstellar hydroxyl masers at VLBI
resolution. A total of 184 Zeeman pairs are identified, and the corresponding
magnetic field strengths are indicated. We also present spectra of the NH3
emission or absorption in these star-forming regions. Analysis of these data
will be presented in a companion paper.
