The efficiency with which transgenic mice can be produced via pronuclear injection of DNA constructs is subject to a large number of variables ranging from human to mechanical to biological. Transgenic core facilities, which are often run like small businesses that must attract and satisfy clients, would benefit from knowing how their efficiency compares to that of other facilities, and whether significant improvements in any phase of the process can be realistically achieved. Communicating knowledgeably with clients about the amount of variation to expect at each step is also important in maintaining good working relationships. We describe a world-wide survey of transgenic core facilities designed to estimate the average yields that can be expected at each step in the process, as well as the inherent variability at each step. The survey has been conducted with the support of the International Society for Transgenic Technologies (ISTT). Some descriptive statistics, calculated from a subset of the data collected so far, are presented for different strains of mice and types of DNA constructs.