Microsporogenesis and pollen development in one cytoplasmic male‐sterile and four genetic male‐sterile strains of Upland cotton (Gossypium hirsutum L.) were studied in comparison with a male‐fertile variety.In the cytoplasmically male‐sterile Upland cotton with the G. harknessii cytoplasm, there was disorganization of tapetal cells and coalescence of pollen mother cells (PMC's) during the premeiotic stages.In the Ms4 dominant genetic male‐sterile anthers, degeneration of microsporocytes was observed before or shortly after the initiation of prophase I. The tapetal cells were reduced in size in some of the anthers.In another dominant genetic male‐sterile, Ms7, meiosis appeared normal in the majority of the PMC's. The abortion of microspores was noticed during formation of the pollen wall. There was no observable malfunctioning of the tapetum.In the double recessive ms5ms6 male‐sterile anthers, vacuolation of developing microspores led to their degeneration. Nutrient deficiency of several kinds might have been the cause of vacuolation and abortion of pollen.In Rhyne's double recessive male‐sterile unthers, premature degeneration of the tapetum caused the abortion of pollen in most locules. In a few locules viable pollen was produced but the anthers were nondehiscent. Seeds were produced when pollen from the indehiscent anthers was released by crushing and dusted on other male‐sterile plants.