A gamma ray tomograph has been designed for the study of the modes of flow in dense phase pneumatic pipelines. The instrument has six americium-241 gamma ray sources and thirty miniature sodium iodide detectors arranged symmetrically around a pipe section. The instrumentation system comprises a multi-channel preamplifier, a CAMAC crate containing multi-channel discriminators, scalers and a GPIB crate controller, and an IBM-compatible personal computer. The detector gains are individually controlled by analogue voltage outputs provided by multi-channel DAC interface cards. The detector count-rates are used with a filtered linear back-projection algorithm to estimate the distribution of solid material over the pipe cross-section at a rate of ten images per second in real time. Preliminary laboratory tests have been carried out on a fluidised bed formed inside a permeameter tube and a full-scale test pipeline and instrument room have been developed for conveying tests.