McCune-Albright syndrome (MAS) is a sporadic disorder characterized by the classic triad of polyostotic fibrous dysplasia, café-au-lait' skin pigmentation, and hyperfunctional endocrinopathy. It is caused by embryonic somatic mutations leading to the substitution of His or Cys for Arg at amino acid 201 of the alpha-subunit of the signal transduction protein Gs (Gsalpha). A 32-year-old man was diagnosed as McCune-Albright syndrome with the following findings: polyostotic fibrous dysplasia, café-au-lait' spots and acromegaly. An ultrasonic examination showed that he had left-pleural effusion, which disappeared after almost a year without special treatment. Genomic DNA was isolated from the peripheral blood, bone tissue, skin lesion and pleura samples of the patient. Then PCR and direct sequencing were performed. An activating mutation of the Gsalpha gene (Arg201Cys) was found in the genomic DNA isolated from the peripheral blood and the bone tissue, but not in genomic DNA isolated from the skin and pleura samples.