The biotechnology of recombinant protein production is now entering its most advanced stage, and the growth of industrial protein pharmaceuticals provides solid proof of this evolution. However, the systematic conversion of genetic information into a biologically active protein is constantly confronted by the fundamental problem of protein folding in cells, and many recombinant proteins are not produced in their native state. Instead, they aggregate into a biologically inactive state. Although this aggregation reaction has some practical advantages, in vitro renaturation of recombinant proteins, after solubilization of cellular aggregates, is still an empiric and random process. Thus, it is better to control cellular expression conditions to minimize this problem inside the cells. The most attractive approach is certainly the development of high throughput genetic screens to monitor efficient protein folding.