The numbers and length of centriole-associated microtubules of two patients with Chediak-Higashi syndrome (CHS) were examined. Detergent- extracted whole-mount preparations of adherent cells were studied by stereo high-voltage electron microscopy. Under conditions of random migration, neutrophils from both patients had a microtubule organization similar to that of the control; microtubule numbers (28 +/- 3) and length (7.0 +/- 2.8 micron) were within normal range. When cells were treated with phorbol myristate acetate (PMA), differences in the response of the two patients were noted. Neutrophils from patient No. 2 and the control showed a significant rise in numbers (38 +/- 5) and length (9.5 +/- 3.6 micron) of microtubules. In contrast, neutrophils from patient No. 1 were unresponsive to PMA treatment. Because vitamin C is used therapeutically in CHS patients and has been shown to correct microtubule-related cell function, neutrophils were exposed to ascorbic acid. A significant increase in microtubule numbers (35 +/- 6) was observed in cells from the control and patient No. 2 after ascorbate treatment; neutrophils from patient No. 1 showed no increase in microtubule numbers. While ascorbic acid did not affect microtubule length in the control cells, it caused a significant increase in microtubule length in neutrophils from both patients. Results suggest that adherent CHS neutrophils contain centriole-associated microtubules which are normal in number and length. However, differences between patients are observed regarding neutrophil responsiveness to stimuli which induce microtubule polymerization.