Ectoine is a small compound synthesized in the cytoplasm of halophilic and halotolerant bacteria in response to salt stress. The compound has been found to behave as a compatible solute counterweighing osmotic imbalance between the interior and exterior of a cell. Because of its positive effects on the water balance of cells and its protective properties ectoine isolated from bacteria is broadly used in medical therapies and biotechnology, e.g. as an additive in cosmetics. The goal of this study was to synthesize ectoine in the chloroplast of the unicellular green alga Chlamydomonas reinhardtii in order to increase the cells salt tolerance. In bacteria synthesis of ectoine is catalyzed by proteins encoded by the ectA, ectB and ectC genes. As the ectC gene was thought to be dispensable for ectoine synthesis in Chlamydomonas, only the bacterial ectB and ectA genes were stably inserted by biolistic transformation into the chloroplast genome of the alga. The resulting transgenic cell lines were investigated and analysed by DNA and RNA blotting techniques for the presence of the genes in the chloroplast genome, for accumulation of ectA and ectB transcripts, and for improvements in salt tolerance due to ectoine accumulation. The results showed that the introduced ectA and ectB genes were expressed in C. reinhardtii but no improvements in salt tolerance of the transformants could be detected. It is concluded that expression of ectA and ectB in the chloroplast of C. reinhardtii is not sufficient for ectoine accumulation. It is suggested that further work focuses on additional expression of the ectC gene and on codon optimization of ectA and ectB genes.