Restricted ocular myasthenia gravis (OMG) and generalised myasthenia gravis (GMG) have been shown to differ in a number of respects. In OMG, antiacetylcholine receptor, antistriational and antinuclear antibodies were rare relative to their frequency in GMG. In contrast, antithyroid antibodies and a history of thyroid disease were much more prevalent in OMG than in GMG, OMG was not associated with the female predominance seen in GMG and appeared to be relatively common in some races rather than others. It is suggested that different pathogenetic mechanisms are responsible for these two forms of MG.