Acquired acanthocytosis (AA) is an uncommon disease characterized by the presence of abnormal red cells (acanthocytes) in the blood smears of affected subjects. Acanthocyte membrane is enriched in cholesterol by an abnormal plasma lipoprotein. We studied the existence of similar changes in platelets of one patient with AA. Red cell cholesterol/phospholipid (Ch/PL) ratio in the patient was 1.6 (normal 1.1 +/- 0.1). Phosphatidylcholine (PC) comprised 36% of total phospholipid (30.7 +/- 1.8% in controls). Platelets showed aberrant morphology in the blood smears, and the ratio Ch/PL was high in comparison with normal platelets (1.4v0.6 +/- 0.1). PC comprised 52% of total PL (39.6 +/- 1.9% in normal platelets). Normal platelets incubated with autologous plasma for 24h maintained a Ch/PL ratio of 0.7, whereas this value changed to 1.4 when these cells were incubated with plasma from the patient. These results suggest that platelets of patients affected by AA acquire the same biochemical abnormality as red cells.