HOx concentrations in the upper tropical troposphere can be enhanced by the presence of acetone and the convective injection of peroxides. These enhancements in HOx might be expected to increase ozone production by increasing the rate of the HO2+NO reaction. We show however that the convective enhancements of hydrogen peroxide (H2O2) and methyl hydroperoxide (CH3OOH) above steady state during the PEM West B campaign were largely restricted to air parcels of marine boundary layer origin in which the mean NO concentration was 8 pptv. The ozone production efficiencies of the two peroxides at such low NO concentrations are very small. Their impact on the ozone budget of the upper tropical troposphere during PEM West B was therefore probably modest. Unlike the peroxides, acetone in the upper tropical troposphere during PEM West B exhibited a positive correlation with NO. It also has a much larger ozone production efficiency than either H2O2 or CH3OOH. It therefore has a much greater potential for significantly increasing ozone production rates in the upper tropical troposphere. ¿ 1998 American Geophysical Union