The marker variable technique is an easy-to-use technique for estimating the magnitude of method bias within a study. However, its validity has not yet been established. This paper addresses three issues assessing the validity of the technique and finds that it is subject to significant validity threats. A redefinition of the marker variable correlation is proposed, which partly addresses the theoretical critiques of the technique. The findings confirm Podsakoff et al.’s (2003) critique that the marker variable technique does not capture key sources of method bias. Implications of the findings for estimating and controlling for method bias within individual studies are addressed.