A new analytical system that uses the rotational signatures of gas phase molecules is described and demonstrated. It uses a solid state source to probe molecular systems in the millimetre and submillimetre wave range, the only region of the electromagnetic spectrum not yet used extensively for analytical purposes. It employs the FAst Scan Submillimetre Spectroscopy Technique (FASSST), which leads to an especially simple system architecture. Among the attributes of the system are generality, sensitivity, 'absolute' specificity, small size, simplicity, and the potential for very low cost. Applications to problems of analytical interest are also discussed.