First, our concern over the potential misinterpretation of 0 ng/ml by clinicians is not negated by the detailed description of how Dr. Wisner and colleagues handled their data set. The interpretation of serum concentrations in nursing infants, in the absence of treatment-emergent side effects, should be both conservative and scientific. To report that an infant’s serum concentration was 0 ng/ml on the basis of either visual or computer interpretation of a chromatograph of ultraviolet absorption would be a less conservative interpretation. To date, all antidepressants studied are found in the breast milk of women taking the medication; the infant is exposed, regardless of infant serum concentration. Further, Dr, Wisner and colleagues reported infant serum concentrations as whole numbers (e.g., not as decimals). This implies that 0.1–0.4 ng/ml could be regarded as 0 ng/ml; they acknowledge as much with the statement "within instrumental limitations." We agree that the limits of detection and quantification are not the same, but they are the lowest value that can be reported. In analytic chemistry, "0" does not exist, and the limits of the assay (be it detection or quantification) convey the most scientific representation of the data (3). The description of categorical division on the basis of infant serum concentration is interesting but fails to address our concern that clinicians may misinterpret the data.