The calicheamicins are a sub-family of enediynes that were isolated from Micromonospora echinospora calichensis. All calicheamicin family members demonstrate potent antimicrobial activity against Gram-positive and Gram-negative organisms. Calicheamicin γ1 exhibited significant antitumor activity against leukemia and melanoma cells in vivo. The calicheamicins are notably similar in structure to the esperamicins.</p>