When cells of the unicellular cyanobacterium <em>Gloeocapsa alpicola</em> CALU 743 are deprived of nitrate, the phycobilisomes are actively degraded by a proteolytic process termed chlorosis, which accompanied by decrease of rates of oxygen evolution and carbon dioxide fixation, increase of amount of stored glycogen and increase of hydrogenase activity. Suspensions of such cells exhibited a capacity for light-dependent inorganic carbon photoassimilation under anaerobic conditions in the presence of hydrogen and DCMU. The rate of <mml:math alttext="${}^{{\text{14}}} {\text{C}}$" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mtext></mml:mtext><mml:mrow><mml:mtext>14</mml:mtext></mml:mrow></mml:msup><mml:mtext>C</mml:mtext></mml:mrow></mml:math> incorporation was commensurable with that for nitrate-sufficient cells at oxygenic photosynthesis and reached 35–38 <mml:math alttext="$\mu $" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>μ</mml:mi></mml:math>mol <mml:math alttext="${}^{{\text{14}}} {\text{C}}$" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mtext></mml:mtext><mml:mrow><mml:mtext>14</mml:mtext></mml:mrow></mml:msup><mml:mtext>C</mml:mtext></mml:mrow></mml:math><mml:math alttext="${\text{h}}^{{\text{ - 1}}} $" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mtext>h</mml:mtext><mml:mrow><mml:mtext>-1</mml:mtext></mml:mrow></mml:msup></mml:mrow></mml:math><mml:math alttext="${\text{mg}}^{ - 1} $" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mtext>mg</mml:mtext><mml:mrow><mml:mn>-1</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math> Chl <em>a</em>. Incubation of <em>G</em>. alpicola grown aerobically in the presence of limiting concentrations of nitrate under anaerobic conditions (Ar, <mml:math alttext="${\text{CO}}_{\text{2}} $" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mtext>CO</mml:mtext></mml:mrow><mml:mtext>2</mml:mtext></mml:msub></mml:mrow></mml:math>, DCMU) in the light with addition of nitrate and <mml:math alttext="${\text{H}}_{\text{2}} $" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mtext>H</mml:mtext><mml:mtext>2</mml:mtext></mml:msub></mml:mrow></mml:math>, resulted in the increase of cellular protein, evidencing that <em>G. alpicola</em> cells with high level of hydrogenase activity are able to perform <mml:math alttext="${\text{H}}_{\text{2}} $" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mtext>H</mml:mtext><mml:mtext>2</mml:mtext></mml:msub></mml:mrow></mml:math>-dependent anoxygenic photosynthesis at levels supporting the growth of this cyanobacterium.