Measurements of ozone made over Canada during the first four months of 1993 indicate that total ozone has been about 11 to 17% below normal. These low values were recorded, without exception, at all nine of the Canadian mid-latitude ground-based monitoring sites. Record low averages for the period from January to April were measured at three of the four mid-latitude stations where measurements have been made since the 1960's. Comparison of January to April, 1993 ozonesonde profile measurements with those from earlier years indicates that the ozone deficit is in the lower stratosphere between 40 and 200 mb, the same altitudes where aerosols from the Mount Pinatubo volcanic eruption have been observed. The peak loss is 30% at 100 mb (16 Km). ¿ American Geophysical Union 1993