There is scientific evidence to suggest that the medicinal mushroom Agaricus blazei Murrill (AbM) has immunomodulatory effects on cytokine synthesis, both in vitro and in vivo. This study was the first randomized, double-blind, placebo-controlled trial designed to investigate these purported actions in elderly women. The objective of this study was to ascertain the effects of AbM intake on serum levels of interleukin-6 (IL-6), interferon-gamma (IFN-γ) and tumour necrosis factor-alpha (TNF-α) in community-living seniors. The sample consisted of 57 elderly females who were carriers or homozygous for the majority allele of functional polymorphisms for the chosen cytokines. Subjects were randomly allocated to receive placebo (n = 29) or AbM dry extract (n = 28), 900 mg/day for 60 days. Body mass index, abdominal girth, body composition, blood pressure and cytokine (IL-6, IFN-γ, and TNF-α) levels were measured, and food intake was assessed as a possible confounder. Analysis of these parameters showed the sample was characterized by overweight and excess adiposity. After the study period, no changes from baseline were detectable for any parameter in either group. In this study, AbM extract had no modulating effect on IL-6, IFN-γ or TNF-α levels in elderly females.