ABSTRACT: We obtained time-resolved, medium resolution (∼1.5 Å) optical (6200–7100 Å) spectra of the low mass X-ray binary (LMXB) Sco X-1 during 2000 April 7–10 on the CTIO 1.5-m telescope. In addition to the well-known Hα emission line, our observations showed an absorption feature near Hα. Absorption lines in active LMXBs are very rare and, to our knowledge, have never been seen in Sco X-1. The absorption feature is shallow, centered redward of the emission line, and possibly varies in depth and/or velocity during the orbit. We repeated our observations of Sco X-1 with the identical instrument setup during 2001 June 15–18, with the addition of simultaneous BVI photometry on the CTIO 0.9-m telescope. It was noted early on (Westphal et al. 1968, Cowley & Crampton 1975) that the Balmer lines dramatically increase in strength when Sco X-1 is faint. We now find an Hα absorption feature that appears only when Sco X-1 is in the bright state.