Suggested method for sequential reporting of results of RQ-PCR assays. Interpretation (assuming adequate quality RNA): (1) BCR-ABL detectable at a level greater than 1.0%, which suggests that the patient has some or 100% Ph-positive marrow metaphases (the patient may still be responding to therapy or may be relapsing from a Ph-negative status); (2) BCR-ABL detectable at a level greater than 0.1%, which suggests that the patient has not achieved or has lost a major molecular response; (3) BCR-ABL detectable at or below the level of 0.1% indicates achievement of a major molecular response (as defined by the IRIS study); and (4) BCR-ABL is not detectable, meaning that the BCR-ABL level is below the level of sensitivity of the assay, which should be at least 0.01% on the international scale, a value equivalent to a 4-log reduction below baseline. The laboratory value for a given result can be converted to a value on the international scale by use of a conversion factor. This factor is based on the relationship of the laboratory specific value for an MMR to the value equivalent to an MMR as established in the IRIS trial, namely a 3-log reduction below an internationally agreed standardized baseline. The conversion factor will be specific for each laboratory but may be affected by any change in the technical aspects of the assay. If the quality of the RNA is poor, no useful conclusion can be drawn from the results of the test.