Total ozone data are statistically analyzed to estimate the trend detection capability which would provide early warning of ozone depletion. Based on a worldwide sample of nine stations, an abnormal gobal ozone chane of 0.26% per year persisting over 6 years would be judged statistically significant, if it were to occur and could not be explained by historical patterns. A resulting 1.56% early warning can limit maximum reversible depletion to 2.3%, if the cause were due to chlorofluoromethanes FC-11 and FC-12. The analysis shows no evidence of an abnormal global trend persisting in the 1970's. The potential exists for detecting even smaller changes by using data froom all the current land-based stations and satellites.