This paper examines cellular and molecular mechanisms that may underpin the purported effects of five herbal supplements in the context of athlete immune function. Ginseng and echinacea are used frequently by athletes, whereas astragalus and elderberry are used infrequently and pequi is just emerging as a possible supplement. In vivo studies of these products on athlete immune function have yielded heterogeneous results, likely due to experimental design differences. Ginseng, echinacea, elderberry, and pequi are considered asterids sensu lato. Ginseng appears to exert strongest effects on components of adaptive immunity, in particular maintaining Th1/Th2 balance of CD4+ T cells and their downstream effects, via its ginsenosides, flavonoids, and polysaccharides. Echinacea alkamides, caffeic acid derivatives, and polysacchardies may target both innate and adaptive immunity, though perhaps the former more consistently. Elderberry harbors anthocyanins and lectins which may modulate innate immunity. Data on pequi is limited but suggests that carotenoids, phenols, and fatty acids may alter circulating leukocyte populations. More phylogenetically distant, astragalus is a rosid sensu lato and may influence the innate immune system through flavonoids, polysaccharides, and saponins. Supplements generally demonstrate no effects on physiologic parameters such as lactate, oxygen dynamics, or athletic performance. Bioavailability studies indicate that purported bioactive molecules of these supplements may reach circulation in low but therapeutically-relevant quantities. Difficulties in cross-comparisons due to study design differences, coupled with an overall dearth of research on the topic, currently hamper any formal conclusions regarding the efficacy of these supplements as immunoregulators for athletes.