The present study has evaluated 46 members from four generations of a large family with mild to moderate bleeding symptoms, prolonged bleeding times and poor responses to all aggregating agents. Twenty-one members of the family had all of the abnormal structural features of the disorder brought to Minnesota in 1870 by Esther White and, therefore, referred to as the White platelet syndrome (WPS). Their platelet counts were decreased and mean platelet volumes increased. Four to 13% of their platelets contained large, fully developed Golgi complexes actively budding smooth and coated vesicles and frequently associated with centrioles. Such structures are usually present in megakaryocytes only during the major phase of granulopoiesis. As many as seven Golgi complexes and five centrioles were present in single platelets. Alpha granule formation appeared incomplete in patient platelets. The organelles were often immature in appearance and markedly decreased in number in many of their cells. As a result 30% or more of WPS platelets were 'gray platelets' similar to, yet very different from the cells in patients with the gray platelet syndrome. Other abnormal features included cytoplasmic sequestration by residual dense tubular system membranes, autodigestion, larger than normal mitochondria and half normal-sized dense bodies. Thirteen of the 46 family members had a 'touch' of WPS. Three to 5% of their platelets contained Golgi complexes. However, gray platelets were not present among their circulating cells. The WPS is a unique autosomal dominant condition that can be classified among the platelet granule deficiency disorders.