Twenty-three fresh tumor specimens obtained at surgery and 5 serially transferable human tumor xenografts were implanted subcutaneously into nude mice and mice with severe combined immunodeficiency (SCID) to compare the take rates of the fresh surgical specimens and the growth rates of the transferable strains. The overall take rates were 65% for the SCID mice and 60% for the nude mice, without any significant difference, although colon carcinoma seemed to have higher acceptance in the SCID mice with a take rate of 6/8. All the serially transferable strains were successfully accepted in the SCID mice, their growth rates being essentially identical to those in the nude mice. These results indicate that the SCID mouse can be used as a human tumor xenograft-mouse system as well as the nude mouse.