From the fall of 1991 through the summer of 1992 the Mauna Loa Observatory Photochemistry Experiment 2 (MLOPEX 2) took place in Hawaii. The experiment consisted of four intensive research periods, each approximately 1 month in duration. We report a comparison of measurements of atmospheric hydroperoxide and methylhydroperoxide as measured during MLOPEX 2a (September 16 to October 23, 1991) and MLOPEX 2b (January 15 to February 15, 1992). The analytical techniques used for measuring hydroperoxides included tunable diode laser infrared absorption (TDLAS) and fluorescence from an enzymatically produced dimer. The TDLAS technique measured hydrogen peroxide (H2O2) only. Three different procedures were utilized to distinguish between H2O2 and organic hydroperoxides in the fluorescence analytical techniques. These were high performance liquid chromatographic (HPLC) separation, enzymatic discrimination, and differential aqueous solubility. The measured concentrations ranged from 0 to 2 parts per billion by volume (ppbv) for H2O2 and 0 to ppbv for methylhydroperoxide (CH3OOH). Depending on the time period of measurement, the agreement varied between 20% and a factor of 2 or more for the measurement of H2O2. The discrepancy for the CH3OOH data was larger. ¿ American Geophysical Union 1996