Materials and Methods

Mice.-All mice were from inbred strains maintained at the Jackson Laboratory, Bar Harbor, Maine, except that mice of strain B10. S were kindly provided by Dr. J. Stimpfling, McLaughlin Laboratories, Great Falls, Mo. The standard inbred strains and the congenic resistant partner strains employed were: A/WySn, A. CA, A. SW, AKR/J, AKR. M, C57BL/10ScSn,(hereinafter abbreviated B10), B10. A, BI0. A (2R), B10. A (5R), B10. AKM, B10. BR, B10. D2/n, B10. M, B10. RIII (71NS), B10. S, B10. WB, C3H/HeDiSn, C3H. SW, C3H-II-2, DBA/IJ, D1. C, LP. RIII, and SJL/J. The haplotypes of these strains are shown in the tables. 13 haplotypes were represented, of which 6 (H-2 a, H-2 h, II-2, H-2. ia, II-2 m, and

H-2) are known or presumed recombinants. Strain A/J was sometimes sub3tituted for A/WySn and C57BL/6J for C57BL/10ScSn. Minor non-H-2 differences between the latter two strains have been revealed by tail skin grafts (DW Bailey, personal communication), but we have noted little differences using body skin grafts (21). Strain C3H-II-2 was originally backcrossed to C3H/HeJSt, but the last two backcrosses were to C3H/HeDISn. We shall hereafter refer to the strains without the substrain symbols and for strains C57BL/10ScSn and C57BL/6J use the abbreviations B10 and B6, respectively.