Studies of changes in platelet tocopherol in 16 children with mucocutaneous lymph node syndrome (MCLS) were undertaken during the disease course. Plasma tocopherol was lowest at the beginning of the disease (during the first 1 to 2 weeks), while it increased with improvement in symptoms at 4 to 5 weeks. Platelet tocopherol however was lowest in the first 2 to 3 weeks, and at about the 4th week or later increased. When compared with normal levels, determined in 24 children without MCLS (5 to 14 years old), the lowest level seen throughout the disease course coincided with it. Thus, platelet tocopherol may be generally higher in MCLS. There was little correlation between plasma and platelet tocopherol levels which were simultaneously assayed, (r = 0.26, p less than 0.1, n = 44), while, the correlation between platelet tocopherol and plasma tocopherol/total lipid ratio was increased significantly to 0.55 (p less than 0.001, n = 38). Individual patients in whom platelet tocopherol and plasma tocopherol/total lipid ratios were repeatedly assayed, were divided into two groups based on the Asai scoring, as a high risk group and a low risk group. No correlation was observed between the risk grades and either platelet tocopherol or tocopherol/total lipid ratios in plasma.