Protein based therapeutics have enjoyed great success over the past decade. Unfortunately, with this clinical success comes a heavy price tag, owing to the inherently high costs of capitalization and production using mammalian cell fermentation. To address this problem, we have begun developing a system for the expression of recombinant proteins in the unicellular eukaryotic green algae, Chlamydomonas reinhardtii, leading to the production of human IgA single chain antibodies. The expression of human monoclonal antibodies in C. reinhardtii offers an attractive alternative to traditional mammalian based expression systems for several reasons, including an ability to rapidly obtain stable plastid and nuclear transformants, coupled with inherently low costs of capitalization and production.