During August and September 1993 a laser-induced fluorescence (LIF) instrument was used to observe OH and HO2 as part of the Tropospheric OH Photochemistry Experiment (TOHPE) in the mountains west of Boulder, Colorado. A prototype version of this instrument has been described previously. Modifications were made to the instrument for TOHPE, including the integration of a new dye laser. The instrument was calibrated by producing known amounts of OH and HO2 above the instrument inlet. HO2 was measured on 19 days during TOHPE, while OH was measured on 5 days. Although poor laser performance limited the detection limit to 1 to 2¿106 cm-3 for an integration time of 300 s and a signal-to-noise ratio of 1, OH concentrations were observed to reach 3 to 7¿106 cm-3 near midday. HO2 typically peaked near 1¿108 cm-3. HO2 consistently reached its maximum near local noon. Observations made with the LIF instrument are compared with observations made with an ion-assisted technique.¿ 1997 American Geophysical Union