The meiotic drive chracteristics of the In(1)sc-4Lsc-8R/Y system have been examined by genetic analysis and by light and electron microscopy. sc-4sc8-/Y males show a direct correlation between nondisjunction frequency and meiotic drive. Temperature-shift experiments reveal that the temperature-sensitive period for nondisjunction is at meiosis, whereas that for meiotic drive has both meiotic and post-meiotic components. Cytological analyses in the light and electron microscopes reveal failures in spermiogenesis in the tests of sc-4sc-8 males. The extent of abnormal spermatid development increases as nondisjunction becomes more extreme.