The spindle checkpoint guards against chromosome segregation errors by delaying the onset of anaphase in cells whose spindles are defective. This mechanism is activated in Drosophila primary spermatocytes in which microtubule dynamics has been disrupted with colchicine (1) or taxol (2). We are using time-lapse video microscopy to follow male meiosis in several Drosophila mutants in which different spindle components are damaged. By measuring the duration of prometaphase-I in these mutant backgrounds in the presence or absence of microtubule poisons we can determine the extent to which these mutations compromise the spindle checkpoint. 1.-Rebollo and Gonzalez, 2000. EMBO reports. 1:65-70. 2.-Savoian et al. 2000. Nat Cell Biol 2:948-952