Infrared solar absorption recorded at 0.002--0.003 cm-1 resolution in the 10 μm region during two recent balloon flights from near 32¿N latitude have been analyzed to determine the isotopic ratios of 16O16O18O and 16O18O16O, the two most abundant forms of isotopically substituted ozone, relative to normal ozone, in the stratosphere. The analysis has used recent improvements in the line parameters for 16O3, 16O16O18O, and 16O18O16O. Normalized to the standard isotopic ratios in ozone, the results show column-averaged isotopic enhancement ratios of 1.20¿0.14 and 1.40¿0.18 for 16O18O16O/16O16O16O and 16O16O18/16O16O16O, respectively, above 37 km altitude for flight measurements on November 18, 1987, and corresponding values of 1016¿0.08 and 1.25¿0.12 for flight measurements on June 6, 1988. These measurements are the first such results obtained at high altitude using infrared techniques. The values are compared with heavy-to-normal O3 ratios reported previously from other techniques. ¿ American Geophysical Union 1989