Male meiotic sterile mutations were selected among X-linked male-steriles by detection of micronuclei in early spermatids. Despite severe defects in the 1st or 2nd meiotic spindles in all mutants, no effect on mitosis was observed. Various features of spindle structure, chromosome segregation, and centriole movements were compared in seven meitoic steriles and in XO males. Chromosome behaviour and centriole movement were always affected concomitantly, and were both shown to be genetically independent of "centre" formation in the meiotic spindles. Precocious and delayed centromere separation was observed in the various mutants in both divisions, and similarly attributed to basic spindle lesions rather than chromosome defects. Attachment of the centriole body to the membrane of the spermatid nucleus was normal only in mutants where second division nuclei were formed. The role of the centriole body was shown to be independent of membrane attachment.--The phenomena observed in this study were discussed mainly with regard to genetic interdependence of morphogenetic processes during male meiosis. A common base for the pleiotropic defects of meiotic steriles and XO males is suggested, and the genetic control of meiosis is re-evaluated in the light of comparison with fertile meiotic mutants.