A European series of 287 cases of "pure" peripheral neuropathy, pooled from 14 neuropediatric centres, has been analysed retrospectively with particular emphasis on the hereditary motor and sensory neuropathies (HMSN) which comprised 241 of the patients. Due to incomplete information in many records it has only been possible to make a crude analysis of the problems of diagnosis and classification. More than half of the HMSN series conform to the diagnosis of HMSN I (charcot-Marie-Tooth-Roussy-Levy disease), A relatively homogeneous group but with large variations in age of onset and severity of disease between individuals in the same family. In five of the 147 cases the onset was at or before birth. An overdiagnosis of HMSN III (Déjérine-Sottas' disease) was considered probable due partly to an unawareness of the high frequency of subclinical carriers among parents in families with HMSN I. Cases with axonal types of polyneuropathy, appearing sporadically or with suspected autosomal dominant (HMSN II) or recessive inheritance, occurred with unexpected frequency in children. This group of 60 pooled European cases was considered worthy of a particularly thorough follow-up and further investigation in order to achieve a better delineation between different subtypes. Cases with an onset before birth or very early in infancy (20 cases) comprised a heterogeneous group with some special subtypes. Surprisingly enough, no less than 5 of the 20 cases represented HMSN I. Cerebrospinal fluid protein levels were not found to be useful for differentiating various types of HMSN. Elevated levels were revealed in about half of the examined cases of HMSN I and in 75% of cases of HMSN III, the levels of increase showing a marked overlap. In nearly all of the axonal cases investigated the CSF protein was normal.