Agrobacterium-mediated transient expression is a recently developed approach to quick and inexpensive large-scale production of recombinant proteins in plant systems. In the course of this process, foreign gene expression occurs during several days after agroinfiltration without integration of recombinant DNA into plant genome and the level of target protein synthesis may be considerably higher than in stably transformed plants. This mini-review describes biological peculiarities of transient expression process, method development and optimization, and the range of application for biotechnological production of variable proteins. Patenting the transient expression protocols that mostly occurred during new millennium indicates the growing interest to this method as a perspective alternative to "classical" pro- and eukaryotic systems for recombinant protein production.