The architecture of gene regulatory networks is reminiscent of electronic circuits. Modular building blocks that respond in a logical way to one or several inputs are connected to perform a variety of complex tasks. Gene circuit engineers have pioneered the construction of artificial gene regulatory networks with the intention to pave the way for the construction of therapeutic gene circuits for next-generation gene therapy approaches. However, due to the lack of a critical amount of eukaryotic cell-compatible gene regulation systems, the field has so far been limited to prokaryotes. Recent development of several mammalian cell-compatible expression control systems laid the foundations for the assembly of transcription control modules that can respond to several inputs. Herein, three approaches to evoke combinatorial transcription control have been followed: (i) construction of artificial promoters with up to three operator sites for regulatory proteins, and (ii) parallel and (iii) serial linking of two gene regulation systems. We have combined tetracycline-, streptogramin-, macrolicle-, and butyrolactone transcription control systems to engineer BioLogic gates of the NOT IF-, AND-, NOT IF IF-, NAND-, OR-, NOR-, and INVERTER-type in mammalian cells, which are able to respond to up to three different small molecule inputs. BioLogic gates enable logical transcriptional control in mammalian cells and, in combination with modern transduction technologies, could serve as versatile tools for regulated gene expression and as building blocks for complex artificial gene regulatory networks for applications in gene therapy, tissue engineering, and biotechnology. (C) 2004 Wiley Periodicals, Inc.