The Zw10 and Rough Deal (Rod) proteins form a complex that is necessary for accurate chromosome segregation during mitosis and meiosis. The complex helps target cytoplasmic dynein to the kinetochore; furthermore, the complex is important to the spindle checkpoint because mutations in zw10 or rod abrogate the metaphase block induced by the checkpoint in cells treated with microtubule inhibitors. We have recently used immunoaffinity chromatography coupled with mass spectroscopy to identify other members of the Zw10/ROD complex. Through these means we discovered a novel protein we have named Zwilch. The Zwilch protein localizes to kinetochores and kinetochore microtubules in a fashion identical to that displayed by Zw10 and Rod. In addition, zwilch mutations cause many of the same cell division phenotypes associated with zw10 and rod mutations. We are also currently investigating another protein suggested by immunoaffinity chromatography to be associated with ZW10. Finally, during the course of a large scale genetic screen we have identified mutations in yet other genes required for the activity of the spindle checkpoint. Several of these mutations, like those in zw10, rod, and zwilch, result in precocious sister chromatid separation during mitosis.