It has been noted that cyanobacteria alter their shape or produce mucilaginous envelopes as a response to environmental changes in NaCl concentration. Such mucilaginous envelopes somehow isolate them from their surroundings. In this paper the effects of NaCl concentration on growth and morphology of Synechococcus sp. A0185001PS are studied. The organism was isolated from the artificial Solar Fields located at Araya in eastem Venezuela. It is believed that this cyanobacterium is one of the organisms that affect salt production. The phenomenon occurs when the organism produces great quantities of mucilage which prevent formation of large salt crystals. Cultures were made with enriched seawater at NaCl concentrations of 0,5 to 3,0 M; continuos light 50 ± 5 µE m-2s-2: temperature of 26 ± 0,5 °C: and constant aeration of 200 ml.min-1. Growth was evaluated by daily determination of population density with a Petroff-Hauser counting chamber. Cell dimensions were estimated simultaneously. It was found that an increase in NaCl concentration from 0,5 to 3,0 resulted in a growth rate decrease from 1,3 to 0,5 div.day-1. A change in shape and size from subspherical (6,3 x 5,5 µm) to cylindrical (10,6 x 6,9 um) was also observed. The results confirm that morphological and morphometric parameters must not be used exclusively to indentify cyanobacterial species.