Two cases of severe myasthenia gravis are described, with histological findings. Both cases showed severe neurogenic atrophy of the muscles of the tongue, with fatty pseudohypertrophy and a remarkable proliferation of terminal nerve fibres. Similar, but less severe, changes were present in other bulbar muscles. The findings are in keeping with the view that functional interruption at the neuromuscular junctions results first in failure to transmit the contractile impulse, and at a later stage in denervation atrophy. Terminal proliferation of axons is regarded as an attempt, on the part of motor fibres, to compensate for the breakdown of normal neuromuscular interaction.