© 2004 Lawrence Erlbaum Associates. All rights reserved. Measurement of workload is a critical element of any research involving operator tasking in complex systems. One common method of measuring workload is through secondary tasking, which requires a subject to use spare mental capacity to attend to secondary tasking. Traditional secondary tasking testing can be intrusive and introduce an unrealistic artifact. However, embedded secondary tasks do not fundamentally change the task or task performance. This paper will discuss the use of a chat interface, resembling that of popular instant messaging programs, as an embedded secondary tasking measurement tool in the testing of supervisory control performance for monitoring and control of Tactical Tomahawk missiles. The use of the embedded chat tool to induce information-seeking secondary tasks yielded critical results needed for determination of operator workload. However one drawback discovered is that some subjects treated incoming instant messages as the primary task instead of the secondary, which degraded overall tasking performance.