CD36 deficiency was studied with attention to the phenotype-genotype relationship. The diagnosis of CD36 deficiency was made when CD36 was negative on platelets (type II) or on both platelets and monocytes (type I). Among 827 apparently healthy Japanese volunteers, the type I and II deficiencies were found in 8 (1.0%) and 48 (5.8%), respectively. The T for C substitution at nt478 for Pro90Ser and the insertion of A at nt 1159 constituted the major causes of type I and II deficiencies. The dinucleotide deletion at nt539 had a minor role. In two family studies, we found a previously unreported polymorphic site in the 5'-proximal flanking region and the 3'-untranslated region. Including these new polymorphisms, DNA sequence other than the three known mutations affecting CD36 expression was not observed in the CD36 gene, calling into question the previous hypothesis that a platelet-specific silent allele exists near or at the CD36 gene.