Lexmark Unison 521 Standard Yield Return Program Black toner cartridge features the Unison Toner's unique formulation that consistently delivers outstanding image quality, ensures long-life print system reliability and promotes superior sustainability all in an innovative, shake-free print system. Genuine Lexmark toner is engineered to work best together with your Lexmark printer, delivering excellent print quality from the first page to the last. Cartridge is designed for use with Lexmark MS810de, MS810dn, MS810dtn, MS810n, MS811dn, MS811dtn, MS811n, MS812de, MS812dn and MS812dtn. Lexmark Return Program cartridges are patented print cartridges sold at a discount in exchange for the customer's agreement to the license requirement that the cartridges will be used only once and returned only to Lexmark for remanufacturing or recycling. These patented cartridges are licensed for single use only and will stop working after delivering a fixed amount.