Measurements of [O III] emission in Lyman-break galaxies (LBGs) at z > 3 are presented. Four galaxies were observed with narrowband filters using the near-IR camera on the Keck I 10 m telescope. A fifth galaxy was observed spectroscopically during the commissioning of NIRSPEC, the new infrared spectrometer on Keck II. The emission-line spectrum is used to place limits on the metallicity. Comparing these new measurements with others available from the literature, we find that strong oxygen emission in LBGs may suggest subsolar metallicity for these objects. The [O III] 位5007 line is also used to estimate the star formation rate (SFR) of the LBGs. The inferred SFRs are higher than those estimated from the UV continuum, and may be evidence for dust extinction
