Three-day-old neonatal rats had their common peroneal nerve crushed 3 mm from the extensor digitorum longus (EDL) muscle. At periodic intervals of 7, 10, 14, 21 and 28 days following nerve injury the EDL muscles were removed, weighed, stained using the silver cholinesterase method and their muscle fibres counted. In these rats during the re-innervation process, the bands of Biingner were absent, some endplates disintegrated and a large proportion of the muscle fibres were lost. This study has shown that interruption of the normal nerve-muscle interaction during the neonatal period is highly detrimental to the subsequent growth and development of the muscle.