Cyanobacteria are able to grow at a wide pH range and for many strains their growth is enhanced in alkaline environment. In this study, we investigated the proteomic response of the cyanobacterium of Synechocystis sp. PCC 6803 to alkaline pH. The proteomes of Synechocystis grown in BG-11 medium buffered at pH 7.5, pH 8.2 and pH 9.2 were analysed by a mass spectrometry-based (LC-MS/MS) data-dependent acquisition (DDA) method. Total proteins (membrane and soluble) from unfractionated Synechocystis cell lysates were investigated.