During different periods of time between 1991 and 1996 we have achieved ground-based observations of rotational lines of atmospheric ozone using two different ground-based radio telescopes located in southern Europe: the 30 meters IRAM radio telescope at Pico Veleta (latitude 37:04:05.60 ¿N, longitude 3:23:58.10 ¿W, altitude 2850 m) and POM-2 at Plateau de Bure, (Hautes Alpes, France, latitude 44:38:02.00 ¿N, longitude 5:54:28.50 ¿E, altitude 2550 m). A total of eight different ozone lines have been observed with frequencies in the range 142-359 GHz. Several back-end spectrometers were able to analyze the incoming signal with very different frequency resolutions and total spectral coverage. This has allowed us to retrieve information about the vertical profile of ozone over a relatively wide range of altitudes. The retrieval itself has been achieved by means of a nonlinear least squares fit of the observed line profile, taking into account the spectroscopic, observational, and instrumental parameters of the different observations. A comparison between the ozone amounts retrieved from observations of different ozone lines in winter and summertime is given separately. Ozone amounts obtained from the different instruments and ozone lines are consistent. ¿ 1998 American Geophysical Union