Previous findings (N. Pecoraro, J. Chou-Green, & M. F. Dallman, 2003; N. Pecoraro & M. F. Dallman, 2005) indicated that unexpected reductions in sucrose concentration in once daily meals result in a febrile response on the 1st, but not the 2nd day of a concentration shift. This study shows that this day-specific fever is blocked by adrenalectomy accompanied by constant low corticosterone replacement. Rats implanted with telemetry probes were adrenalectomized and given low-corticosterone pellets or were sham operated. Food-restricted rats were given 2 rounds of sucrose concentration downshifts, as follows: 32% sucrose (14 days), 4% sucrose (6 days), 32% sucrose (4 days), and 4% sucrose (4 days). Intact rats showed more pronounced anticipation of the sucrose than did rats having low, clamped corticosterone. Only intact rats showed a 4-hr, postshift temperature burst on the 1st, but not the 2nd day of the shift to 4% sucrose, during both rounds of shifting. Increased activity accompanied the fever. These data confirm previous findings, show them to be dependent on high corticosterone, and appear to be related to a host of day-specific alterations in other motor outflows following unexpected downward shifts in palatable sucrose concentrations.