Given the degree of complexity of modern magnetotelluric (MT) instrumentation, comparison of the total performance for two or more systems is an important verification test. This paper compares the processed data from five MT systems which were designed and constructed separately, and which employ different electrode types, electrode separations, magnetometers, and methods of signal processing. The comparison shows that there is a high degree of agreement among the data from the different systems. The study also demonstrates the compatibility and reliability of the MT systems employed as part of EMSLAB Juan de Fuca (Electromagnetic Sounding of the Lithosphere and Asthenosphere Beneath the Juan de Fuca Plate). This project, proposed by a consortium of institutions, involves not only magnetotellurics studies but also studies of magnetic variation, on land and on the sea bottom. The project calls for the real‐time MT systems to occupy stations along segments of a profile in Oregon. A composite profile will be created from the segments. Prior to commencing the main MT profiling phase, one week was set aside in August, 1984, for all groups to record and process MT data sequentially at six sites in diverse geologic terrains; this experiment was called mini‐EMSLAB.