A summary of the spectral characteristics of the LANDSAT-4 and LANDSAT-5 Thematic Mapper instruments, the protoflight (TM/PF) and flight (TM/F) models, respectively, is presented. Data collected by the Hughes/Santa Barbara Research Center on the instruments and their components to determine compliance with the spectral coverage and spectral matching specifications served as the basis for the characterization. Compliance with the spectral coverage specifications (e.g. band locations) was determined by deriving band-by-band relative spectral response (RSR) curves from spectral measurements on the individual components contributing to the overall spectral response: filters, detectors and optical surfaces. The integrated system RSRs were not measured. The derived RSRs for the reflective bands were similar between TM/PF and the TM/F. The bandpasses between 50 per cent RSR points varied by only 2nm at most between the sensors and were: band 1, 452-518 nm; band 2, 528-609 nm; band 3, 625-693 nm; band 4, 776-904 nm; band 5, 1568-1784 nm and band 7, 2097-2348 nm. The upper-band edge of band 5 was outside the desired and specified range of 1750 ±20 nm; this implies that there will be more contribution from variable atmospheric water vapour absorption. In the emissive thermal band 6, the TM/PF and TM/F showed fundamentally different spectral responses. Though the lower band edges were both at approximately 104/mi, the TM/PF upper-band edge was detector limited at a temperature-dependent value of about 11·7μm, whereas the TM/F upper-band edge was filter limited at 12·4μm. Despite the TM/PF's band 6 narrow bandwidth, its radiometric performance exceeded requirements, so the band's narrowness was not a serious concern. Spectral matching measures the spectral differences between channels within a band by calibrating them all with one source and comparing their outputs to a spectrally different source. Satisfactory TM/PF spectral matching data were never obtained. TM/F channels were shown to have comparable or better spectral matching than past and existing MSS sensors.