For utilization of the mouse embryonic stem (ES) cells for various purposes, it is desirable that the cell lines are established from various sources such as inbred and mutant mouse strains. So far, however, most ES cell lines used in genetic manipulation have been derived from the 129/Sv strain. We have established ES cell lines from blastocysts of the C57BL/6 strain at high efficiency by use of a fibroblast cell line SL10 as feeder cells, and supplementing the culture medium with 5,000 unit/ml LIF. Using such culture conditions, we have also established a number of ES cell lines from the BALB/c, BXSB/MpJ-Yaa and MRL/Mp-lpr/lpr mouse strains. Procedure for establishment of ES cell lines had to be modified among the mouse strains, indicating the strain difference. For example, only a few stem cell colonies appeared from the BALB/c blastocysts. Stem cells of the BXSB strain were very sensitive to the trypsinization in subculturing. Most of these cell lines had normal karyotype and produced chimeric mice. Several C57BL/6 cell lines contributed to the germ-line. These results indicate that ES cell lines can be established from various mouse strains, but their characteristics are different among strains.