Various biological markers that function as indicators of the level of senescent cells in an organism are provided. In certain embodiments, the markers described herein (e.g., eicosanoids) can provide effective indicators of the presence and/or quantity of senescent cells in a subject (e.g., in a human or non-human mammal) and methods of identifying elevated levels of senescent cells in a mammal, and methods for determining the efficacy of senolytic agents, are provided.
