A mouse ENU-mutagenesis program at RIKEN GSC has been initiated to conduct a large-scale, genome-wide, early- and late-onset phenotypic screen of mutant mice. We screened about a hundred mice every week with a comprehensive set of phenotype assays including behavioral tests based on a modified SHIRPA protocol, blood tests (both clinical biochemical testing and hemogram), and measurement of locomotor activity in their home cages. To manage the entire program, we developed a client/server architecture database system and named it MUSDB (Mutagenesis Universal Support DataBase). It manages mouse husbandry, mating protocols, procedures for ENU injection and phenotypic screens, phenotype inheritance tests, preservation of sperm and organs, and other materials generated during the program. We have implemented MUSDB in quite a large-scale system that includes 150 client computers. It has, helped reduce typographical errors and provided simple and efficient operation via its front-end user interface. It significantly contributed to the communication within and between workgroups in the program and in the accumulation of various phenotypic and inheritance data.