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Lead disrupts heme synthesis by inhibiting δ-ALA dehydratase and ferrochelatase, contributing to microcytic anemia and basophilic stippling; it can also cause neurologic and renal injury. Mercury binds sulfhydryl groups and may injure neurons and renal tubules, with tremor, neuropsychiatric changes, and gingivostomatitis among its classic findings. Arsenite inhibits lipoic acid–dependent enzymes, while arsenate uncouples oxidative phosphorylation. Acute arsenic toxicity can cause severe gastrointestinal illness and shock; chronic exposure is associated with characteristic skin changes, neuropathy, and increased cancer risk. Exposure history, targeted laboratory testing, and appropriate chelation are central themes across the topic.