Spindle pole bodies, basal bodies and centrosomes are morphologically quite different structures that nevertheless perform similar microtubule-organizing functions in diverse cell types. The recent discoveries that both centrins and gamma-tubulin are common components of these structures suggest a molecular basis for their common functions. The role of centrins is just beginning to be investigated. These filament-associated proteins bind Ca2+. The filaments contract at least in certain circumstances by an ATP-independent mechanism. However, yeast centrin is clearly involved in the duplication of the spindle pole body. A common molecular mechanism may underlie these two apparently different functions.