T4 levels in inbred parental strains and recombinant inbred (RI) mice. A and B, Total T4 (T-T4) for C3H/He, BALB/c (abbreviated C3H and BALB, respectively), A, DBA/2 (abbreviated DBA), and B6 strains. T-T4 values are for female mice (5–13 weeks old); mean + sem for C3H (n = 15), BALB (n = 9), A (n = 14), DBA/2 (n = 14), and B6 (n = 15). *, P < 0.05; significantly different from T-T4 levels in B6 mice (ANOVA). Deiodinase type-1 (D1) activity, plotted from the data of Berry et al. (13), is for predominantly male mice. C–F, T-T4 in AXBXA, CXB, BXD, and BXH RI strains. Data are shown as the mean + sem for n = 3 or more, sd for n = 2. The numbers of sera studied were as follows: BXD n = 3–5 (except BXD 16, n = 2; BXD13, n = 1); BXH n = 6 (except BXH11 and cC3, n = 2); CXB n = 4 (except CXB5, n = 2); AXBXA n = 2. T-T4 data for CXB, BXH, C3H, and B6 strains were presented previously as “preimmunization” values (4, 5).