Mobile Remote Presence (MRP) technologies make it possible for the user to be mobile in a remote environment, which opens up new possibilities for interaction. However, this new functionality comes at a cost. The need for MRP system users to pay attention to both telecommunication and device navigation increases their cognitive load. Assessing the cognitive load of MRP system users is a timely research issue, which is addressed in this paper both conceptually and empirically. We argue that Secondary Task (ST) techniques have certain advantages over existing Subjective Rating Scales (SRS) instruments, and report a study, in which a particular ST technique, a visual monitoring task, was employed to assess MRP pilot's cognitive load. The empirical evidence from the study indicates that the method provides additional valuable insights into MRP pilots' user experience.