Values represent the number of mast cells in each combination of donors and recipients. Results are mean ± SE of 5 mice and are given as the number per 10³ peritoneal cells, number per mm² mesentery and spleen, and number per cm stomach and skin. The number of mast cells in each combination of donors and recipients was less than 0.1 for B6-tg/tg to WBB6F₁-W/W^v mice. P < .01 by t test when compared with the values observed in WBB6F₁-W/W^v mice transplanted from B6-+/+ donors. WBB6F₁-W/W^v mice were irradiated with 2 Gy before transplantation.