Cyanobacteria are important primary producers in marine and other aqueous ecosystems. Members of the genus Synechococcus are globally distributed and exhibit high potential for acclimatisation and adaptation to diverse environmental conditions. The inter-disciplinary research project Endosymbiont (University of Bremen) proposes to utilize Synechococcus for the establishment of novel biomedical therapies based upon survival and growth under human physiological conditions. The main objective of the project is to successfully introduce living cyanobacterial cells into human keratinocytes (epidermal skin cells) in a quasi-stable functional coexistence. Such photosynthetic, endosymbiotic cells would then be able to produce oxygen and consequently promote wound healing in tissues with impaired perfusion. In this work, one marine and one freshwater strain of Synechococcus were characterised with respect to their short-term growth and tolerance to different culturing conditions,such as temperature, pH and salinity ranges mimicking certain aspects of the cytosol of human keratinocytes. The marine strain Synechococcus sp. RCC2384 (Red Sea) was not able to grow at salinities lower than 100% of the artificial seawater medium. The freshwater strain Synechococcus sp. PCC7942 showed sufficient tolerance to selected osmotic conditions, with growth rates between 2.4 ± 0.64 day-1 (0% salinity), 1.7 ± 0.23 (10%),2.6 ± 0.51 (20%) and 0.84 ± 0.3 day-1 (30%) during initial exponential growth at 30 °C. The pH that the medium was initially adjusted to had no effect on the actual pH measured in the cultures presumably due to the reduced carbonate buffer system in medium of lower salinity. However, the pH at time t0 had significant effects on the subsequent growth rates (t0 – t1), and the pigment signal strength at t1. This indicated a pH sensitivity regarding growth and physiological health that could not be fully evaluated for targeted pH values in this work. Nevertheless, a more acidic pH at t0 led to higher growth rates and lower pigment fluorescence when normalised to cell concentrations. The osmotic condition likely had an indirect effect on both parameters by widening the possible pH range. Due to the adaptability shown here for Synechococcus sp. PCC7942 for osmotic concentration and pH range from below pH 7.0 up to pH 10.0, the strain emerges as the ideal candidate for potential future medical application.