A recent study by Mitrovic and Schachner (J Neurosci Res 42:710-717, 1995) reported the detection of a small amount of truncated tensacin-C (TN-C) in the nervous system of the TN-C knockout mice created by Saga et al. (Genes Dev 6:1821-1831, 1992). The authors suggested that the truncated protein might be responsible for the failure to detect any phenotypic abnormalities in the knockout mice. We have reexamined the knockout mice in our laboratories by Western blot and immunocytochemistry, and have not detected any full-length or truncated TN-C protein. In addition, we note that the construction of the knockout gene deleted the signal sequence, so if any residual truncated protein were produced it would be trapped in the cytoplasm, and therefore inaccessible to extracellular ligands or receptors. We therefore conclude that the TN-C knockout created by Saga et al. is a valid TN-C null.