Immune changes in 75 younger (age 37.4 ± 0.9 years) and 23 older (57.0 ± 1.4 years) runners were compared after a competitive marathon, with blood samples collected pre- and immediately and 1.5 hr postrace. Race times were slower for the older group (4.7 ± 0.2 vs. 4.3 ± 0.1 hr, p = .015), but both groups performed at similar intensity (83.4 ± 0.9 vs. 82.9 ± 0.5% HRmax). The pattern of change in plasma cortisol, epinephrine, growth hormone, and blood leukocyte subsets did not differ significantly between the groups postrace. Blood lymphocyte counts were 20–24% lower in the older runners at each time point because of reduced T-cell counts. Postrace, plasma levels of IL-1ra, -10, -6, and -8 rose strongly in all runners, and salivary IgA secretion rate decreased, but no group differences in the pattern of change were noted. In conclusion, younger and older runners experienced similar hormonal and immune changes after running a marathon.