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Blue-green algae (Cyanobacteria) are imponant to the ecology of arid rangelands as sources of nitrogen and as soil stabilizers, yet have been the subject of little comment or investigation in Australia. To provide information on their distribution soil samples were collected from 136 locations in rangeland areas of southem Australia and cultured to permit the identification of the blue-green algae present. Blue-green algae were found in 134 of the samples. The species represented include several apparently capable of nitrogen fixation, and all produce a gelatinous sheath which can bind soil panicles to produce soil-surface crusts. It is likely that lichens and blue-green algae are important for the ecology of arid rangelands now, and if climatic change destroys the lichens which are very heat sensitive when wet, blue- greens may become even more significant in soil conservation and the maintenance of pasture productivity. Both lichens and blue-green algae merit inclusion in assessments of range condition.