A polymorphism in codon 52 of the human thyrotropin receptor results in a proline to threonine substitution in the extracellular domain of the receptor, and it has been suggested that the rarer, 52Thr, allele is associated with susceptibility to Graves' disease in the female population. To investigate this association we analyzed the distribution of TSH-R alleles in male (n = 60) and female (n = 120) Graves' patients, and control subjects (male n = 160 and female n = 85), using a PCR amplification and mismatch oligonucleotide hybridization technique. The variant allele was present in 8.3% of patients and 7.3% of control subjects. The frequencies in male and female patients were 6.7 and 9.2% respectively, and the allele distribution did not differ significantly from that observed in controls. No association was found between this TSH-R polymorphism and the occurrence of Graves' disease in the male or female population.