There Is disagreement over the HLA-DR associations of Hashimoto's (goitrous) thyroiditis. We have studied 86 English Caucasian patients with this condition whose DR types were determined by restriction fragment polymorphism analysis. HLA-DR3 was significantly more frequent In these patients than in 100 controls (χ2= 7·09; P > 0·01). The relative risk was 2·23 and aetiological fraction 0·29. HLA-DPB and DOB alleles were analysed in a proportion of these subjects by enzymatic DNA amplification and oligonucleotide probing. The only significant finding was an excess of HLA-DQw2 (In linkage disequllibrium with DR3) In the Hashimoto group (χ2=7·43, P > 0·007). These results do not support a difference between goitrous and atrophic thyroiditis based on respective associations with HLA-DR5 and DR3, but confirm a recent study in which HLA-DR3 was associated with Hashimoto's thyroiditis. However, It Is possible that genes telomeric to DR3 may be Involved in determining which type of thyroiditis a patient with autoimmune hypothyroidism develops.