Reversible changes between limiting and high inorganic carbon regimes in Synechocystis PCC6803 maintained overall protein synthesis at a high level. The protein patterns of cells during or after adaptation to these regimes were detected by pulse labelling and identification after one‐dimensional and two‐dimensional electrophoreses. Several particular patterns were observed. Proteins specific for either the high or the limiting carbon conditions could be identified. The protein profiles of cells having reached the stationary phase of growth clearly differed from those of their exponentially growing counterparts. Accumulation of Rubisco, the key enzyme of the Calvin cycle, was not modified in the conditions tested.