Abstract MAGION (1978-099C) was launched as a part of the Interkosmos 18 satellite and separated from this parent spacecraft on 14 November 1978, with the aim of studying the spatial structure of ELF-VLF phenomena using simultaneous measurements of the two near-spaced satellites. The MAGION experiment went on for almost three years, till the decay date of September 10, 1981. A description of the experiment is given and some new aspects of the satellite-subsatellite experimental technique for near-space research are indicated.