The prevalence of auto-antibodies against thyroid constituents, gastric parietal cells, smooth muscle cells, mitochondria, reticulin, nuclear constituents and rheumatoid factor in 108 patients with alopecia areata was compared with that found in a previous survey of the local population. Female patients had a significantly increased prevalence of anti-thyroid antibodies which were present in 30% overall and in 44% of the youngest age group (11-17 years). Smooth muscle antibodies were more frequent in female patients but the increase was not significant. Male patients had a significant increased prevalence of thyroid and gastric parietal cell antibodies (11.4% each). In females, antithyroid antibodies were associated with extensive hair loss: they were found in 42% of female patients with total alopecia and only 20% of males with total hair loss. A family history of alopecia areata was obtained from 24% of patients; 10% had relatives with thyroid disease and 10% had diabetic relatives. These findings confirm the association between alopecia areata and the other auto-immune diseases.