Key characteristics of male reproductive toxicants. Exposure to male reproductive toxicants (MRT) resulting in (1) altered spermatogenesis, normal functions (e.g., acrosome reaction), or increased cell death; (2) disruptions in somatic cell development (e.g., increased or decreased proliferation), functions (e.g., alterations in blood–testis barrier), or death; (3) changes in hormone production/levels; (4) modifies hormone receptor functions/cellular levels; (5) increases DNA damage; (6) epigenetic alterations of cellular macromolecules (DNA, RNA, and/or proteins); (7) reactive oxygen species (ROS)-induced cellular damage; and (8) increases inflammation (e.g., elevated production/levels of pro-inflammatory cytokines and edema). In combination with the male-specific end points of reproductive toxicity described in Table S1, the key characteristics of male reproductive toxicants can be applied for the evaluation of toxicological and mechanistic evidence for hazard identification.